Hrm, but a ref is a file containing a hash, right? So if the hash is equivalent to the file, the surely a ref is equivalent to a symlink? A symbolic ref, in turn, should be a symlink to a symlink... Or something like that...

A ref points to an object. That object doesn't change unless the hashing algo was tricked.

A branch points to anything you want it to point to. It can be any ref you want and can be changed at will.

sha1 - object (e.g. 5a480efb...) file with sha1 - ref (e.g. master) file with ref - symbolic ref (e.g. HEAD)

right? Seeing as you can git update-ref branches, but you need to git symbolic-ref HEAD.

But it is a ref. It's an alias for the last commit of a particular timeline, as I said above.

So would you rather say a branch is a commit?

A branch is a pointer or symlink if you will.