fan

fan n.  Without qualification, indicates a fan of science
   fiction, especially one who goes to {con}s and tends to hang out
   with other fans.  Many hackers are fans, so this term has been
   imported from fannish slang; however, unlike much fannish slang it
   is recognized by most non-fannish hackers.  Among SF fans the
   plural is correctly `fen', but this usage is not automatic to
   hackers.  "Laura reads the stuff occasionally but isn't really a
   fan."