verb (used without object) 1.to reply to an invitation: Don't forget to RSVP before Thursday.
noun 2.a reply to an invitation: He sent a lovely bouquet of flowers with his RSVP.
3.(used on an invitation to indicate that the favor of a reply is requested).
Also, R.S.V.P.
Origin:
1895–1900; < French r(épondez) s('il) v(ous) p(laît) please reply