I've received some "bonus" performance related equity grants with a four year vesting period. These are beyond normal the refresher grants. They are not described by the company as "bonus", because we also have the sort of cash bonus you're talking about, but were I to describe them to people outside the company, I'd probably say "bonus grants" or something.

In this case it seems obvious that it needs some kind of vesting terms to prevent people from taking the bonus and then just taking another offer anyways.