The letters RSVP are a symbol of "Repondez s'il vous plait" a French term meaning "Please Respond" or "Please Reply". You'll frequently find these letters at the end of the invitation for casual occasions like kids birthday parties or baby showers. For additional formal occasions, the invitation package usually includes a unique RSVP card. The RSVP card signifies your company name (the invitee) therefore the host can easily see who the RSVP card comes from, the amount of guests in (if you are likely to bring a guest along with you) and also the very explicit "I'll attend" and "I won't attend" tick boxes.
Exactly why hosts include them within an invitation happens because when you finish studying with the particulars specified by the invitation, such as the time and date from the event, the place or even the venue where it will likely be held as well as for whom the party has been tossed, then you'll have the ability to look at your own schedule, verify your plans and choose whether you are likely to attend or otherwise. The RSVP particulars will also be pretty forthcoming which means you genuinely have no excuse to not act upon the RSVP.