That's kind of the simplest case, though, where "theirs" and "ours" makes obvious sense.

What if I'm rebasing a branch onto another? Is "ours" the branch being rebased, or the other one? Or if I'm applying a stash?

> What if I'm rebasing a branch onto another?

Just checkout the branch you are merging/rebasing into before doing it.

> Or if I'm applying a stash?

The stash is in that case effectively a remote branch you are merging into your local codebase. ours is your local, theirs is the stash.