RSVP literally means "Please respond", however it seems to have turned itself into a noun in common usage:
"What's your RSVP for the party?"
Is it acceptable to refer to a person's attendance status as their RSVP ?
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The conventional meaning of the abbreviation is (from New Oxford American Dictionary):
répondez s'il vous plaît, or please reply (used at the end of invitations to request a response)
Modern usage of the term has pushed the boundaries of its use, and the Corpus of Contemporary American English includes examples of it being used as pretty much everything form a noun, a verb, an adjective, etc.
- It said to RSVP with the enclosed card
- Rosie O'Donnell's last-minute RSVP is throwing everyone into a tizzy
- There's an RSVP section
- When people RSVP with uninvited dates, I deal with that
- I think it's the third request for your RSVP in regard to your alma mater's fundraiser
It appears as such in fiction, magazines and printed news, so you can consider it's pretty common (though not particularly formal).