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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.