Usually means an obsessed superfan but have evolved to mean someone with unwavering support of a person or entity. Came from the Eminem song "Stan" about a crazy fan.
>The name of the eponymous character has given rise to a slang term online which refers to overzealous, maniacal, overly obsessed fans of a celebrity or personality; the term has been included in the Oxford English Dictionary.
https://en.wikipedia.org/wiki/Stan_(song)
>The name of the eponymous character has given rise to a slang term online which refers to overzealous, maniacal, overly obsessed fans of a celebrity or personality; the term has been included in the Oxford English Dictionary.