fan n.
Without qualification, indicates a fan of science fiction,
especially one who goes to cons 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."