Revisions
Many Git commands take revision parameters as arguments. Depending on the command,
they denote a specific commit or, for commands which walk the revision graph (such
as git log), all commits which are reachable from that commit. For commands that
walk the revision graph one can also specify a range of revisions explicitly.
In addition, some Git commands (such as git show) also take revision parameters
which denote other objects than commits, e.g. blobs ("files") or trees ("directories
of files").