R.S.V.P. or r.s.v.p.
American SlangDefinition
Abbreviation of the French “Répondez s’il vous plaît,” meaning “please respond”; a request to confirm whether you will attend an event (also used as a verb meaning to reply).
Examples
"Please R.S.V.P. by Friday so we can finalize the headcount."
"The invitation includes an R.S.V.P. card—mail your response by the 10th."
"If you can’t make it, r.s.v.p. to decline so the host can adjust the seating."