the.com/rsvp
A polite French command disguised as four innocent letters demanding you actually decide.
means A request to confirm whether or not you'll attend an event, so the host can plan accordingly.
from Initials of the French répondez s'il vous plaît, meaning please reply, borrowed wholesale into English invitations since the 19th century.
Literal senseIt politely orders you to respond.
Redundant phrasingPlease RSVP technically says please please reply.
Etiquette ruleSilence is a no, not a maybe.