RSVP

I have another one of those puzzling questions for you today....What exactly does RSVP stand for? Its something that we do quite often to all kinds of dinners, parties and events, but what are we actually doing when we RSVP? I know that we are letting someone know whether we are coming of not, but does RSVP actually stand for something? or does it actually have nothing to do with telling someone whether you can come or not and just happens to the phrase we use? I don't know but I would like to so if you know, rsvp and tell me!