Theme nights often refer to costume dress by staff and sometimes passengers. A recent cruise I took featured "Fifties Night" and "Medieval Night". Many passengers got into costume for the Fifties theme at dinner and that night's 'sock hop' and 'drive-in' buffet. For Medieval Night it was mostly the wait staff that donned costumes for dinner and that night's theater production was a "Camelot" style musical. Passengers who didn't want to dress up just wore casual clothes.