In ear monitor, I believe. The "headphones" that some musicians use on stage to hear themselves. I have heard that you can get them custom made to fit your own ears for a perfect fit.
In this context, I’m pretty sure it’s In-Ear-Monitors; or, the headphones that go in your ear.
I’d also disagree that there’s no difference between price/quality of monitors!
Sure, p10 and p80 is going to be huge different. As I said, above p90, it's a lot of illusion and subjective .. more like a taste there.
In-ear monitors - or - earbuds, which are generally going to be wired if using 'IEM' over 'earbuds'.
In Ear Monitors, basically a earbuds that goes inside you ear