[jefftk]

In addition to being narrower than cookies it's also broader: they're phasing out all shared client-side storage in a third-party context. Imagine if a.example and b.example both iframed in a page from c.example. It doesn't matter whether the c.example page uses cookies, localStorage, IndexedDB, or something else: it can't share arbitrary state to recognize that the user on a.example is the same user as the one on b.example.

It's common to use "cookies" to refer to any client side storage because at the time people first started talking about "cookies" the other forms didn't exist yet.

This would all be much clearer if we talked about "cross-site tracking".