If you're wondering what the "M" on an RSVP card means, you're not alone! The "M" is actually the first letter of the guest's title, such as Mr., Mrs., Ms., or Miss. This traditional way of addressing guests on formal invitations helps to ensure that your guests know how to fill out their responses properly. Once your guests have filled in the appropriate title, they should write their full name along with the names of anyone else who has been invited on the line provided. For example, a guest attending the wedding alone should write "Ms. Jane Smith" on the response card. Remember that not all invitations or cultures use the "M" on RSVPs, but it can be a helpful tool for ensuring that your guests feel comfortable and confident in their responses.