[[def_alternate_object_database]]alternate object database::
	Via the alternates mechanism, a <<def_repository,repository>>
	can inherit part of its <<def_object_database,object database>>
	from another object database, which is called "alternate".

[[def_bare_repository]]bare repository::
	A bare repository is normally an appropriately
	named <<def_directory,directory>> with a `.git` suffix that does not
	have a locally checked-out copy of any of the files under
	revision control. That is, all of the Git
	administrative and control files that would normally be present in the
	hidden `.git` sub-directory are directly present in the
	`repository.git` directory instead,
	and no other files are present and checked out. Usually publishers of
	public repositories make bare repositories available.

[[def_blob_object]]blob object::
	Untyped <<def_object,object>>, e.g. the contents of a file.

[[def_branch]]branch::
	A "branch" is an active line of development.  The most recent
	<<def_commit,commit>> on a branch is referred to as the tip of
	that branch.  The tip of the branch is referenced by a branch
	<<def_head,head>>, which moves forward as additional development
	is done on the branch.  A single Git
	<<def_repository,repository>> can track an arbitrary number of
	branches, but your <<def_working_tree,working tree>> is
	associated with just one of them (the "current" or "checked out"
	branch), and <<def_HEAD,HEAD>> points to that branch.

[[def_cache]]cache::
	Obsolete for: <<def_index,index>>.

[[def_chain]]chain::
	A list of objects, where each <<def_object,object>> in the list contains
	a reference to its successor (for example, the successor of a
	<<def_commit,commit>> could be one of its <<def_parent,parents>>).

[[def_changeset]]changeset::
	BitKeeper/cvsps speak for "<<def_commit,commit>>". Since Git does not
	store changes, but states, it really does not make sense to use the term
	"changesets" with Git.

[[def_checkout]]checkout::
	The action of updating all or part of the
	<<def_working_tree,working tree>> with a <<def_tree_object,tree object>>
	or <<def_blob_object,blob>> from the
	<<def_object_database,object database>>, and updating the
	<<def_index,index>> and <<def_HEAD,HEAD>> if the whole working tree has
	been pointed at a new <<def_branch,branch>>.

[[def_cherry-picking]]cherry-picking::
	In <<def_SCM,SCM>> jargon, "cherry pick" means to choose a subset of
	changes out of a series of changes (typically commits) and record them
	as a new series of changes on top of a different codebase. In Git, this is
	performed by the "git cherry-pick" command to extract the change introduced
	by an existing <<def_commit,commit>> and to record it based on the tip
	of the current <<def_branch,branch>> as a new commit.

[[def_clean]]clean::
	A <<def_working_tree,working tree>> is clean, if it
	corresponds to the <<def_revision,revision>> referenced by the current
	<<def_head,head>>. Also see "<<def_dirty,dirty>>".

[[def_commit]]commit::
	As a noun: A single point in the
	Git history; the entire history of a project is represented as a
	set of interrelated commits.  The word "commit" is often
	used by Git in the same places other revision control systems
	use the words "revision" or "version".  Also used as a short
	hand for <<def_commit_object,commit object>>.
+
As a verb: The action of storing a new snapshot of the project's
state in the Git history, by creating a new commit representing the current
state of the <<def_index,index>> and advancing <<def_HEAD,HEAD>>
to point at the new commit.

[[def_commit_object]]commit object::
	An <<def_object,object>> which contains the information about a
	particular <<def_revision,revision>>, such as <<def_parent,parents>>, committer,
	author, date and the <<def_tree_object,tree object>> which corresponds
	to the top <<def_directory,directory>> of the stored
	revision.

[[def_core_git]]core Git::
	Fundamental data structures and utilities of Git. Exposes only limited
	source code management tools.

[[def_DAG]]DAG::
	Directed acyclic graph. The <<def_commit_object,commit objects>> form a
	directed acyclic graph, because they have parents (directed), and the
	graph of commit objects is acyclic (there is no <<def_chain,chain>>
	which begins and ends with the same <<def_object,object>>).

[[def_dangling_object]]dangling object::
	An <<def_unreachable_object,unreachable object>> which is not
	<<def_reachable,reachable>> even from other unreachable objects; a
	dangling object has no references to it from any
	reference or <<def_object,object>> in the <<def_repository,repository>>.

[[def_detached_HEAD]]detached HEAD::
	Normally the <<def_HEAD,HEAD>> stores the name of a
	<<def_branch,branch>>, and commands that operate on the
	history HEAD represents operate on the history leading to the
	tip of the branch the HEAD points at.  However, Git also
	allows you to <<def_checkout,check out>> an arbitrary
	<<def_commit,commit>> that isn't necessarily the tip of any
	particular branch.  The HEAD in such a state is called
	"detached".
+
Note that commands that operate on the history of the current branch
(e.g. `git commit` to build a new history on top of it) still work
while the HEAD is detached. They update the HEAD to point at the tip
of the updated history without affecting any branch.  Commands that
update or inquire information _about_ the current branch (e.g. `git
branch --set-upstream-to` that sets what remote tracking branch the
current branch integrates with) obviously do not work, as there is no
(real) current branch to ask about in this state.

[[def_directory]]directory::
	The list you get with "ls" :-)

[[def_dirty]]dirty::
	A <<def_working_tree,working tree>> is said to be "dirty" if
	it contains modifications which have not been <<def_commit,committed>> to the current
	<<def_branch,branch>>.

[[def_evil_merge]]evil merge::
	An evil merge is a <<def_merge,merge>> that introduces changes that
	do not appear in any <<def_parent,parent>>.

[[def_fast_forward]]fast-forward::
	A fast-forward is a special type of <<def_merge,merge>> where you have a
	<<def_revision,revision>> and you are "merging" another
	<<def_branch,branch>>'s changes that happen to be a descendant of what
	you have. In such these cases, you do not make a new <<def_merge,merge>>
	<<def_commit,commit>> but instead just update to his
	revision. This will happen frequently on a
	<<def_remote_tracking_branch,remote-tracking branch>> of a remote
	<<def_repository,repository>>.

[[def_fetch]]fetch::
	Fetching a <<def_branch,branch>> means to get the
	branch's <<def_head_ref,head ref>> from a remote
	<<def_repository,repository>>, to find out which objects are
	missing from the local <<def_object_database,object database>>,
	and to get them, too.  See also linkgit:git-fetch[1].

[[def_file_system]]file system::
	Linus Torvalds originally designed Git to be a user space file system,
	i.e. the infrastructure to hold files and directories. That ensured the
	efficiency and speed of Git.

[[def_git_archive]]Git archive::
	Synonym for <<def_repository,repository>> (for arch people).

[[def_gitfile]]gitfile::
	A plain file `.git` at the root of a working tree that
	points at the directory that is the real repository.

[[def_grafts]]grafts::
	Grafts enables two otherwise different lines of development to be joined
	together by recording fake ancestry information for commits. This way
	you can make Git pretend the set of <<def_parent,parents>> a <<def_commit,commit>> has
	is different from what was recorded when the commit was
	created. Configured via the `.git/info/grafts` file.

[[def_hash]]hash::
	In Git's context, synonym for <<def_object_name,object name>>.

[[def_head]]head::
	A <<def_ref,named reference>> to the <<def_commit,commit>> at the tip of a
	<<def_branch,branch>>.  Heads are stored in a file in
	`$GIT_DIR/refs/heads/` directory, except when using packed refs. (See
	linkgit:git-pack-refs[1].)

[[def_HEAD]]HEAD::
	The current <<def_branch,branch>>.  In more detail: Your <<def_working_tree,
	working tree>> is normally derived from the state of the tree
	referred to by HEAD.  HEAD is a reference to one of the
	<<def_head,heads>> in your repository, except when using a
	<<def_detached_HEAD,detached HEAD>>, in which case it directly
	references an arbitrary commit.

[[def_head_ref]]head ref::
	A synonym for <<def_head,head>>.

[[def_hook]]hook::
	During the normal execution of several Git commands, call-outs are made
	to optional scripts that allow a developer to add functionality or
	checking. Typically, the hooks allow for a command to be pre-verified
	and potentially aborted, and allow for a post-notification after the
	operation is done. The hook scripts are found in the
	`$GIT_DIR/hooks/` directory, and are enabled by simply
	removing the `.sample` suffix from the filename. In earlier versions
	of Git you had to make them executable.

[[def_index]]index::
	A collection of files with stat information, whose contents are stored
	as objects. The index is a stored version of your
	<<def_working_tree,working tree>>. Truth be told, it can also contain a second, and even
	a third version of a working tree, which are used
	when <<def_merge,merging>>.

[[def_index_entry]]index entry::
	The information regarding a particular file, stored in the
	<<def_index,index>>. An index entry can be unmerged, if a
	<<def_merge,merge>> was started, but not yet finished (i.e. if
	the index contains multiple versions of that file).

[[def_master]]master::
	The default development <<def_branch,branch>>. Whenever you
	create a Git <<def_repository,repository>>, a branch named
	"master" is created, and becomes the active branch. In most
	cases, this contains the local development, though that is
	purely by convention and is not required.

[[def_merge]]merge::
	As a verb: To bring the contents of another
	<<def_branch,branch>> (possibly from an external
	<<def_repository,repository>>) into the current branch.  In the
	case where the merged-in branch is from a different repository,
	this is done by first <<def_fetch,fetching>> the remote branch
	and then merging the result into the current branch.  This
	combination of fetch and merge operations is called a
	<<def_pull,pull>>.  Merging is performed by an automatic process
	that identifies changes made since the branches diverged, and
	then applies all those changes together.  In cases where changes
	conflict, manual intervention may be required to complete the
	merge.
+
As a noun: unless it is a <<def_fast_forward,fast-forward>>, a
successful merge results in the creation of a new <<def_commit,commit>>
representing the result of the merge, and having as
<<def_parent,parents>> the tips of the merged <<def_branch,branches>>.
This commit is referred to as a "merge commit", or sometimes just a
"merge".

[[def_object]]object::
	The unit of storage in Git. It is uniquely identified by the
	<<def_SHA1,SHA-1>> of its contents. Consequently, an
	object can not be changed.

[[def_object_database]]object database::
	Stores a set of "objects", and an individual <<def_object,object>> is
	identified by its <<def_object_name,object name>>. The objects usually
	live in `$GIT_DIR/objects/`.

[[def_object_identifier]]object identifier::
	Synonym for <<def_object_name,object name>>.

[[def_object_name]]object name::
	The unique identifier of an <<def_object,object>>.  The
	object name is usually represented by a 40 character
	hexadecimal string.  Also colloquially called <<def_SHA1,SHA-1>>.

[[def_object_type]]object type::
	One of the identifiers "<<def_commit_object,commit>>",
	"<<def_tree_object,tree>>", "<<def_tag_object,tag>>" or
	"<<def_blob_object,blob>>" describing the type of an
	<<def_object,object>>.

[[def_octopus]]octopus::
	To <<def_merge,merge>> more than two <<def_branch,branches>>.

[[def_origin]]origin::
	The default upstream <<def_repository,repository>>. Most projects have
	at least one upstream project which they track. By default
	'origin' is used for that purpose. New upstream updates
	will be fetched into remote <<def_remote_tracking_branch,remote-tracking branches>> named
	origin/name-of-upstream-branch, which you can see using
	`git branch -r`.

[[def_pack]]pack::
	A set of objects which have been compressed into one file (to save space
	or to transmit them efficiently).

[[def_pack_index]]pack index::
	The list of identifiers, and other information, of the objects in a
	<<def_pack,pack>>, to assist in efficiently accessing the contents of a
	pack.

[[def_pathspec]]pathspec::
	Pattern used to limit paths in Git commands.
+
Pathspecs are used on the command line of "git ls-files", "git
ls-tree", "git add", "git grep", "git diff", "git checkout",
and many other commands to
limit the scope of operations to some subset of the tree or
worktree.  See the documentation of each command for whether
paths are relative to the current directory or toplevel.  The
pathspec syntax is as follows:
+
--

* any path matches itself
* the pathspec up to the last slash represents a
  directory prefix.  The scope of that pathspec is
  limited to that subtree.
* the rest of the pathspec is a pattern for the remainder
  of the pathname.  Paths relative to the directory
  prefix will be matched against that pattern using fnmatch(3);
  in particular, '*' and '?' _can_ match directory separators.

--
+
For example, Documentation/*.jpg will match all .jpg files
in the Documentation subtree,
including Documentation/chapter_1/figure_1.jpg.
+
A pathspec that begins with a colon `:` has special meaning.  In the
short form, the leading colon `:` is followed by zero or more "magic
signature" letters (which optionally is terminated by another colon `:`),
and the remainder is the pattern to match against the path. The optional
colon that terminates the "magic signature" can be omitted if the pattern
begins with a character that cannot be a "magic signature" and is not a
colon.
+
In the long form, the leading colon `:` is followed by a open
parenthesis `(`, a comma-separated list of zero or more "magic words",
and a close parentheses `)`, and the remainder is the pattern to match
against the path.
+
The "magic signature" consists of an ASCII symbol that is not
alphanumeric. Currently only the slash `/` is recognized as a
"magic signature": it makes the pattern match from the root of
the working tree, even when you are running the command from
inside a subdirectory.
+
A pathspec with only a colon means "there is no pathspec". This form
should not be combined with other pathspec.

[[def_parent]]parent::
	A <<def_commit_object,commit object>> contains a (possibly empty) list
	of the logical predecessor(s) in the line of development, i.e. its
	parents.

[[def_pickaxe]]pickaxe::
	The term <<def_pickaxe,pickaxe>> refers to an option to the diffcore
	routines that help select changes that add or delete a given text
	string. With the `--pickaxe-all` option, it can be used to view the full
	<<def_changeset,changeset>> that introduced or removed, say, a
	particular line of text. See linkgit:git-diff[1].

[[def_plumbing]]plumbing::
	Cute name for <<def_core_git,core Git>>.

[[def_porcelain]]porcelain::
	Cute name for programs and program suites depending on
	<<def_core_git,core Git>>, presenting a high level access to
	core Git. Porcelains expose more of a <<def_SCM,SCM>>
	interface than the <<def_plumbing,plumbing>>.

[[def_pull]]pull::
	Pulling a <<def_branch,branch>> means to <<def_fetch,fetch>> it and
	<<def_merge,merge>> it.  See also linkgit:git-pull[1].

[[def_push]]push::
	Pushing a <<def_branch,branch>> means to get the branch's
	<<def_head_ref,head ref>> from a remote <<def_repository,repository>>,
	find out if it is a direct ancestor to the branch's local
	head ref, and in that case, putting all
	objects, which are <<def_reachable,reachable>> from the local
	head ref, and which are missing from the remote
	repository, into the remote
	<<def_object_database,object database>>, and updating the remote
	head ref. If the remote <<def_head,head>> is not an
	ancestor to the local head, the push fails.

[[def_reachable]]reachable::
	All of the ancestors of a given <<def_commit,commit>> are said to be
	"reachable" from that commit. More
	generally, one <<def_object,object>> is reachable from
	another if we can reach the one from the other by a <<def_chain,chain>>
	that follows <<def_tag,tags>> to whatever they tag,
	<<def_commit_object,commits>> to their parents or trees, and
	<<def_tree_object,trees>> to the trees or <<def_blob_object,blobs>>
	that they contain.

[[def_rebase]]rebase::
	To reapply a series of changes from a <<def_branch,branch>> to a
	different base, and reset the <<def_head,head>> of that branch
	to the result.

[[def_ref]]ref::
	A 40-byte hex representation of a <<def_SHA1,SHA-1>> or a name that
	denotes a particular <<def_object,object>>. They may be stored in
	a file under `$GIT_DIR/refs/` directory, or
	in the `$GIT_DIR/packed-refs` file.

[[def_reflog]]reflog::
	A reflog shows the local "history" of a ref.  In other words,
	it can tell you what the 3rd last revision in _this_ repository
	was, and what was the current state in _this_ repository,
	yesterday 9:14pm.  See linkgit:git-reflog[1] for details.

[[def_refspec]]refspec::
	A "refspec" is used by <<def_fetch,fetch>> and
	<<def_push,push>> to describe the mapping between remote
	<<def_ref,ref>> and local ref.

[[def_remote_tracking_branch]]remote-tracking branch::
	A regular Git <<def_branch,branch>> that is used to follow changes from
	another <<def_repository,repository>>. A remote-tracking
	branch should not contain direct modifications or have local commits
	made to it. A remote-tracking branch can usually be
	identified as the right-hand-side <<def_ref,ref>> in a Pull:
	<<def_refspec,refspec>>.

[[def_repository]]repository::
	A collection of <<def_ref,refs>> together with an
	<<def_object_database,object database>> containing all objects
	which are <<def_reachable,reachable>> from the refs, possibly
	accompanied by meta data from one or more <<def_porcelain,porcelains>>. A
	repository can share an object database with other repositories
	via <<def_alternate_object_database,alternates mechanism>>.

[[def_resolve]]resolve::
	The action of fixing up manually what a failed automatic
	<<def_merge,merge>> left behind.

[[def_revision]]revision::
	Synonym for <<def_commit,commit>> (the noun).

[[def_rewind]]rewind::
	To throw away part of the development, i.e. to assign the
	<<def_head,head>> to an earlier <<def_revision,revision>>.

[[def_SCM]]SCM::
	Source code management (tool).

[[def_SHA1]]SHA-1::
	"Secure Hash Algorithm 1"; a cryptographic hash function.
	In the context of Git used as a synonym for <<def_object_name,object name>>.

[[def_shallow_repository]]shallow repository::
	A shallow <<def_repository,repository>> has an incomplete
	history some of whose <<def_commit,commits>> have <<def_parent,parents>> cauterized away (in other
	words, Git is told to pretend that these commits do not have the
	parents, even though they are recorded in the <<def_commit_object,commit
	object>>). This is sometimes useful when you are interested only in the
	recent history of a project even though the real history recorded in the
	upstream is much larger. A shallow repository
	is created by giving the `--depth` option to linkgit:git-clone[1], and
	its history can be later deepened with linkgit:git-fetch[1].

[[def_symref]]symref::
	Symbolic reference: instead of containing the <<def_SHA1,SHA-1>>
	id itself, it is of the format 'ref: refs/some/thing' and when
	referenced, it recursively dereferences to this reference.
	'<<def_HEAD,HEAD>>' is a prime example of a symref. Symbolic
	references are manipulated with the linkgit:git-symbolic-ref[1]
	command.

[[def_tag]]tag::
	A <<def_ref,ref>> under `refs/tags/` namespace that points to an
	object of an arbitrary type (typically a tag points to either a
	<<def_tag_object,tag>> or a <<def_commit_object,commit object>>).
	In contrast to a <<def_head,head>>, a tag is not updated by
	the `commit` command. A Git tag has nothing to do with a Lisp
	tag (which would be called an <<def_object_type,object type>>
	in Git's context). A tag is most typically used to mark a particular
	point in the commit ancestry <<def_chain,chain>>.

[[def_tag_object]]tag object::
	An <<def_object,object>> containing a <<def_ref,ref>> pointing to
	another object, which can contain a message just like a
	<<def_commit_object,commit object>>. It can also contain a (PGP)
	signature, in which case it is called a "signed tag object".

[[def_topic_branch]]topic branch::
	A regular Git <<def_branch,branch>> that is used by a developer to
	identify a conceptual line of development. Since branches are very easy
	and inexpensive, it is often desirable to have several small branches
	that each contain very well defined concepts or small incremental yet
	related changes.

[[def_tree]]tree::
	Either a <<def_working_tree,working tree>>, or a <<def_tree_object,tree
	object>> together with the dependent <<def_blob_object,blob>> and tree objects
	(i.e. a stored representation of a working tree).

[[def_tree_object]]tree object::
	An <<def_object,object>> containing a list of file names and modes along
	with refs to the associated blob and/or tree objects. A
	<<def_tree,tree>> is equivalent to a <<def_directory,directory>>.

[[def_tree-ish]]tree-ish::
	A <<def_ref,ref>> pointing to either a <<def_commit_object,commit
	object>>, a <<def_tree_object,tree object>>, or a <<def_tag_object,tag
	object>> pointing to a tag or commit or tree object.

[[def_unmerged_index]]unmerged index::
	An <<def_index,index>> which contains unmerged
	<<def_index_entry,index entries>>.

[[def_unreachable_object]]unreachable object::
	An <<def_object,object>> which is not <<def_reachable,reachable>> from a
	<<def_branch,branch>>, <<def_tag,tag>>, or any other reference.

[[def_upstream_branch]]upstream branch::
	The default <<def_branch,branch>> that is merged into the branch in
	question (or the branch in question is rebased onto). It is configured
	via branch.<name>.remote and branch.<name>.merge. If the upstream branch
	of 'A' is 'origin/B' sometimes we say "'A' is tracking 'origin/B'".

[[def_working_tree]]working tree::
	The tree of actual checked out files.  The working tree normally
	contains the contents of the <<def_HEAD,HEAD>> commit's tree,
	plus any local changes that you have made but not yet committed.