My 30th birthday party is a week away, and I still have not received firm indications whether some guests plan to attend. Even though, I sent evites 4 weeks prior and clearly stated a specified date by which to R.S.V.P. This could mean either one of two things. First it could mean that rudeness is a growing trend in our society. Or, as I would prefer to believe, people no longer understand what the term means.
What RSVP Means
The term R.S.V.P. comes from the French expression "répondez s'il vous plaît", meaning "please respond".

If an invitation has R.S.V.P, it means the invited guests must tell the host whether or not they plan to attend the party. It does not mean to respond only if you're coming, and it does not mean respond only if you're not coming. The expression "Regrets Only" is reserved for that instance. R.S.V.P means the host needs a definite head count for the planned event, and needs it by the date specified on the invitation.

Why It's Inconsiderate to Not RSVP
An incomplete list of respondents can cause numerous problems for a host including difficulty in planning food and drink quantities, issues relating to minimum guarantees with catering halls, uncertainty over the number of party favors and difficulties in planning appropriate seating, among other things.

So the next time you see R.S.V.P. on an invitation you receive, please contact your host and respond promptly (or at least by the specified R.S.V.P. deadline!

Source: Donna Pilato