WC means toilet — the room, and sometimes the toilet itself. It comes from 'water closet', the old name for a small room with a flushing toilet. Almost nobody says 'water closet' out loud any more; the letters live on mainly on signs, especially in public buildings, train stations, airports, hotels and restaurants, and especially in Europe. Because it is short and neutral, it works well as an international sign — many non-English speakers recognise WC even if they do not read English. But in speech it sounds old-fashioned or foreign in Britain, America, Canada and Australia. If you ask an American 'Where is the WC?' they will understand you, but it will sound odd — they say 'restroom' or 'bathroom'. British speakers say 'the toilet' or 'the loo'. So: read it on signs, but choose a different word when you speak. One more use: house adverts and floor plans use WC for a small room with only a toilet, as in 'a downstairs WC'. Said letter by letter: W-C.