Soon after Eminem's Dido-featuring track "Stan" became a worldwide hit in 2000, the name became slang for a troublingly dedicated fan. Now, "Stan" has entered the Oxford English Dictionary, according to Exclaim!.
The definition lists "Stan" as both a noun and a verb. It can refer to "an overzealous or obsessive fan of a particular celebrity." In a sentence, the noun form could be used thusly: "I am a Jeremy Corbyn stan." As a verb, it means to "be an overzealous or obsessive fan of a particular celebrity," e.g., "I stan for Jeremy Corbyn."
The origin of "Stan" as a word is listed by the OED as "Early 21st century: probably with allusion to the 2000 song “Stan” by the American rapper Eminem, about an obsessed fan."