R.S.V.P. stands for the French phrase répondez s'il vous plaît, which means “please respond.” You'll see these letters on invitations to birthday parties, weddings, or other events where the host needs to know how many people are coming.

When an invitation says R.S.V.P., it's asking you to let the host know whether you'll attend. This is a request you're expected to honor. The host needs this information to prepare the right amount of food, set up enough chairs, or plan activities for the correct number of guests. If twenty people don't bother to R.S.V.P. and then show up anyway, there might not be enough pizza or party favors.

Responding to an R.S.V.P. shows consideration for whoever is planning the event. They're working hard to make everything run smoothly, and they can't do that without knowing who's coming. Usually an invitation will include a date by which to respond, like “Please R.S.V.P. by March 15,” along with a phone number, email, or reply card to make responding easy.

People sometimes use R.S.V.P. as a verb, saying “Did you R.S.V.P. to the party?” when they mean “Did you respond to the invitation?”