Definition from Wiktionary, the free dictionary
Alternative forms 
RSVP (plural RSVPs)
- Initialism of reply please. (written on an invitation to request that the invited person reply to confirm whether or not they will be attending.)
- (computing) Initialism of Resource reservation protocol. (at Wikipedia)
Usage notes 
Properly, used by itself, but often used in the redundant form “please RSVP”, “RSVP” being used to mean “reply to an invitation”. Such redundancy is an example of RAS syndrome.
Coordinate terms 
initialism meaning reply please
- (intransitive) To reply to an invitation.