R.S.V.P.youdaoicibaDictYouDict[R.S.V.P. 词源字典]
also RSVP, c. 1845, from French initialism (acronym) of répondez, s'il vous plait "reply, if you please," as it might have been written on a letter or envelope.[R.S.V.P. etymology, R.S.V.P. origin, 英语词源]