Earbuds like Apple Airpods, Apple Airpods, QianYun Qian69 don’t have eartips or nozzles to go into ear canals. They are generally cheap, mostly have cheap dynamic drivers (moving coil).
IEMs (In ear monitors) are more sophisticated and way more expensive with state-of-the-art design. That’s sound chamber (housings), hardwares -(BA or Dynamic). They are not mass produced like earbuds and often customized to user’s ears. Universal IEMs on the other hand are cheaper, intended for music lovers or singers. And because of price, universal IEMs are more accessible to consumers.
IEMs are mostly used by audio experts or singers who need to MONITOR what people hear at the concert or studios (voice and background music…).