@Felthry Some services called them one, others called them the other, users from both converged onto multiple platforms and the terms have become largely interchangeable I guess.
We should totally coin our own phrase for them and make it even more confusing. We could call them CM's for confidential messages! Then we'll have CM, DM and PM which are all actually just IMs(™).
@Felthry Oooh. PA is extra confusing given its existing use for Public Address, the exact opposite of a PM/CM/DM/IM™.