'Stan' means to be an extremely enthusiastic fan of a celebrity, artist or fictional character. It comes from Eminem's 2000 song of the same name, about an obsessive fan. Today the word has lost its dark edges and just means 'devoted fan'. 'I stan Beyoncé' = 'I'm a huge Beyoncé fan'. Used as a verb ('I stan'), noun ('he's a Taylor stan') and identity. Generally harmless; only worth attention if fandom becomes obsessive or hostile to other fans.