GIT Glossary
============

[[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
	<<def_object_database,object database>>, which is called "alternate".

[[def_bare_repository]]bare repository::
	A <<def_bare_repository,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
	<<def_revision,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 non-cyclical graph of revisions, i.e. the complete history of a
	particular <<def_revision,revision>>, which is called the
	branch <<def_head,head>>. The heads
	are stored in `$GIT_DIR/refs/heads/`.

[[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 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 the <<def_working_tree,working tree>> to a
	<<def_revision,revision>> which was stored in the
	<<def_object_database,object database>>.

[[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 different codebase. In GIT, this is
	performed by "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 <<def_commit,commit>>.

[[def_clean]]clean::
	A <<def_working_tree,working tree>> is <<def_clean,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 verb: The action of storing the current state of the
	<<def_index,index>> in the <<def_object_database,object database>>. The
	result is a <<def_revision,revision>>. As a noun: Short hand for
	<<def_commit_object,commit object>>.

[[def_commit_object]]commit object::
	An <<def_object,object>> which contains the information about a
	particular <<def_revision,revision>>, such as parents, committer,
	author, date and the <<def_tree_object,tree object>> which corresponds
	to the top <<def_directory,directory>> of the stored
	<<def_revision,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,commit>> objects form a
	directed acyclic graph, because they have parents (directed), and the
	graph of <<def_commit,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
	<<def_dangling_object,dangling object>> has no references to it from any
	reference or <<def_object,object>> in the <<def_repository,repository>>.

[[def_dircache]]dircache::
	You are *waaaaay* behind.

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

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

[[def_ent]]ent::
	Favorite synonym to "<<def_tree-ish,tree-ish>>" by some total geeks. See
	`http://en.wikipedia.org/wiki/Ent_(Middle-earth)` for an in-depth
	explanation. Avoid this term, not to confuse people.

[[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
	<<def_revision,revision>>. This will happen frequently on a
	<<def_tracking_branch,tracking branch>> of a remote
	<<def_repository,repository>>.

[[def_fetch]]fetch::
	Fetching a <<def_branch,branch>> means to get the
	<<def_branch,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.

[[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_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 parents a <<def_commit,commit>> has
	is different from what was recorded when the <<def_commit,commit>> was
	created. Configured via the `.git/info/grafts` file.

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

[[def_head]]head::
	The top of a <<def_branch,branch>>. It contains a <<def_ref,ref>> to the
	corresponding <<def_commit_object,commit object>>.

[[def_head_ref]]head ref::
	A <<def_ref,ref>> pointing to a <<def_head,head>>. Often, this is
	abbreviated to "<<def_head,head>>". Head refs are stored in
	`$GIT_DIR/refs/heads/`.

[[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 <<def_hook,hook>> scripts are found in the
	`$GIT_DIR/hooks/` <<def_directory,directory>>, and are enabled by simply
	making them executable.

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

[[def_index_entry]]index entry::
	The information regarding a particular file, stored in the
	<<def_index,index>>. An <<def_index_entry,index entry>> can be unmerged,
	if a <<def_merge,merge>> was started, but not yet finished (i.e. if the
	<<def_index,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 <<def_branch,branch>> named
	"<<def_master,master>>" is created, and becomes the active
	<<def_branch,branch>>. In most cases, this contains the local
	development, though that is purely conventional and not required.

[[def_merge]]merge::
	To <<def_merge,merge>> branches means to try to accumulate the changes
	since a common ancestor and apply them to the first
	<<def_branch,branch>>. An automatic <<def_merge,merge>> uses heuristics
	to accomplish that. Evidently, an automatic <<def_merge,merge>> can
	fail.

[[def_object]]object::
	The unit of storage in git. It is uniquely identified by the
	<<def_SHA1,SHA1>> of its contents. Consequently, an
	<<def_object,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 <<def_hash,hash>>
	of the <<def_object,object>>'s contents using the Secure Hash Algorithm
	1 and usually represented by the 40 character hexadecimal encoding of
	the <<def_hash,hash>> of the <<def_object,object>> (possibly followed by
	a white space).

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

[[def_octopus]]octopus::
	To <<def_merge,merge>> more than two branches. Also denotes an
	intelligent predator.

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

[[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 gitlink: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
	<<def_core_git,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.

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

[[def_reachable]]reachable::
	All of the ancestors of a given <<def_commit,commit>> are said to be
	<<def_reachable,reachable>> from that <<def_commit,commit>>. More
	generally, one <<def_object,object>> is <<def_reachable,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,SHA1>> or a name that
	denotes a particular <<def_object,object>>. These may be stored in
	`$GIT_DIR/refs/`.

[[def_refspec]]refspec::
	A <<def_refspec,refspec>> is used by <<def_fetch,fetch>> and
	<<def_push,push>> to describe the mapping between remote <<def_ref,ref>>
	and local <<def_ref,ref>>. They are combined with a colon in the format
	<src>:<dst>, preceded by an optional plus sign, +. For example: `git
	fetch $URL refs/heads/master:refs/heads/origin` means
	"grab the master <<def_branch,branch>> <<def_head,head>>
	from the $URL and store it as my origin
	<<def_branch,branch>> <<def_head,head>>". And `git <<def_push,push>>
	$URL refs/heads/master:refs/heads/to-upstream` means
	"publish my master <<def_branch,branch>>
	<<def_head,head>> as to-upstream <<def_branch,branch>> at $URL". See
	also gitlink:git-push[1]

[[def_repository]]repository::
	A collection of 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
	porcelains. A <<def_repository,repository>> can share an
	<<def_object_database,object database>> with other repositories.

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

[[def_revision]]revision::
	A particular state of files and directories which was stored in the
	<<def_object_database,object database>>. It is referenced by a
	<<def_commit_object,commit object>>.

[[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]]SHA1::
	Synonym for <<def_object_name,object name>>.

[[def_shallow_repository]]shallow repository::
	A <<def_shallow_repository,shallow repository>> has an incomplete
	history some of whose commits have 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 <<def_shallow_repository,shallow repository>>
	is created by giving the `--depth` option to gitlink:git-clone[1], and
	its history can be later deepened with gitlink:git-fetch[1].

[[def_symref]]symref::
	Symbolic reference: instead of containing the <<def_SHA1,SHA1>> id
	itself, it is of the format 'ref: refs/some/thing' and when
	referenced, it recursively dereferences to this reference. 'HEAD' is a
	prime example of a <<def_symref,symref>>. Symbolic references are
	manipulated with the gitlink:git-symbolic-ref[1] command.

[[def_tag]]tag::
	A <<def_ref,ref>> pointing to a <<def_tag,tag>> or
	<<def_commit_object,commit object>>. In contrast to a <<def_head,head>>,
	a tag is not changed by a <<def_commit,commit>>. Tags (not
	<<def_tag_object,tag objects>>) are stored in `$GIT_DIR/refs/tags/`. 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
	<<def_commit,commit>> ancestry <<def_chain,chain>>.

[[def_tag_object]]tag object::
	An <<def_object,object>> containing a <<def_ref,ref>> pointing to
	another <<def_object,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 <<def_tag_object,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_tracking_branch]]tracking branch::
	A regular git <<def_branch,branch>> that is used to follow changes from
	another <<def_repository,repository>>. A <<def_tracking_branch,tracking
	branch>> should not contain direct modifications or have local commits
	made to it. A <<def_tracking_branch,tracking branch>> can usually be
	identified as the right-hand-side <<def_ref,ref>> in a Pull:
	<<def_refspec,refspec>>.

[[def_tree]]tree::
	Either a <<def_working_tree,working tree>>, or a <<def_tree_object,tree
	object>> together with the dependent blob and <<def_tree,tree>> objects
	(i.e. a stored representation of a <<def_working_tree,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 <<def_tag,tag>> or <<def_commit,commit>> or
	<<def_tree_object,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_working_tree]]working tree::
	The set of files and directories currently being worked on, i.e. you can
	work in your <<def_working_tree,working tree>> without using git at all.