[xelxebar]

Or just gitrevisions(7). The manpage for git(1) mentions this under the section SYMBOLIC IDENTIFIERS. Not that that's the most obvious place to look, but if you rtfm the obvious stuff, you should stumble upon these gems naturally.

It's worth scrounging through git(1) anyway; it mentions several other manpages for things like recommended workflows, the basic structure of the .git/ directory, not to mention gittutorial(7).

[gpvos]

In git(1) it's below LOW-LEVEL COMMANDS (PLUMBING). You cannot expect a novice to read thoroughly past something like that.

And it's remarkably hard to find using web searches, since most git documentation uses the term "commit" for these things, not "revision".[0] I found it after I discovered "git help -g", which lists "some concept guides" according to "git help".

Of course, n=1 and stuff, but there's a lot about git that is not obviously documented. Something like this should be linked to in multiple places, so even if you skim over one you'll catch it relatively early.

[0] The name of the man page was chosen to avoid conflict with the "git commit" command, I guess?