People use RSS to describe the idea; the fact that the actual technology is frequently Atom is poorly understood. People still use “SSL” to refer to tunneled encryption even though the SSL protocol is no longer in common use.

Technical nitpick: JSONFeed is something different and can’t express the full Atom data model.

I n'th the suggestion that “RSS” has annoyingly become the general term for feeds, maybe because the latter term is maybe too generic.

But RSS also has a technical holdout because the major podcasting platforms and players seem to only support RSS. Apple’s Podcasting directory stopped supporting Atom feeds last year. It shouldn't be, Atom feeds can do anything and you can of course use the necessary extension elements in Atom – but culturally the podcasting ecosystem is on this weird road.

I think people use the term RSS pars pro toto for the generic idea of feeds.