It's another word for describing (hardcore) fans.
People who idolize somebody else.
Sometimes the term is used in an offensive way, to 'attack' somebody who is idiolizing another person hardcore.
It's originated from the song Stan by
Eminem. A song that goes about a hardcore
Eminem fan called Stan.
The term has been used in several songs by different artists, like Logic in his song Return.
"
Eminem is so awesome, I'm a
real Stan!"
"Used to call you a hater, you a motherfuckin' Stan"
-
LogicDude why do you idiolize him so much? You're such a Stan