An RSVP invitation includes the name of the person or persons hosting the event; the type and purpose of the event; the date, place and time of the event; the expected manner of dress (if important) and instructions on how to RSVP. The RSVP instructions include clear information about whom to contact in order to RSVP as well as the date by which RSVPs or regrets must be received.
RSVP means "respondez s'il vous plait" in French, which translates to "please respond." It is proper etiquette to respond to such an invitation even if attending the event is not possible. In that instance, the reply stating a guest cannot attend is called "regrets." Some RSVP invitations request only regrets, which means that if those who receive invitations plan to attend the event in question, they do not need to respond.
It is appropriate for an invitee to bring a guest only if the invitation indicates that it is expected. Such invitations usually provide a line on the response card to fill in the number of guests attending. In some situations, invitations are addressed directly to the invitee and his guest. If it is necessary to cancel after accepting an invitation to an event, do it as soon as possible.