What Does the M Mean on an RSVP CARD?

THE “M” on an RSVP card is a traditional etiquette prompt that stands for the first letter of your preferred title (such as Mr., Mrs., Ms., Miss, or Mx.).
It is simply a cue to let you know where to write your name(s) and how you would like to be addressed.
How to Fill It Out
You simply complete the line by writing your title and name(s). For example: