- (informal) To respond to an invitation, usually to indicate that one will be coming to the corresponding event.
- Will you rsvp for the party?
- When did you rsvp to the wedding invitation?
Usage notes 
Generally one rsvps to invitations and rsvps for events, as in the example sentences provided. An RSVP regrets only means that the sender will assume the invited people will come unless they reply.
Alternative forms 
Initialism of répondez s'il vous plaît (“please reply”).
- (at the end of a letter) Please reply.