When you open a wedding invitation and find an RSVP card, there may be one small detail that immediately catches your attention: a line beginning with the letter “M.” If you have never encountered the traditional format before, it can seem like the card is asking you to answer a question. But the meaning is much simpler than it appears.

The “M” is actually the beginning of a courtesy title. Traditionally, guests complete it by adding the rest of the title they prefer, such as “Mr.,” “Mrs.,” “Ms.,” or “Miss,” followed by their name. The practice comes from older formal invitation etiquette, when titles were commonly used when addressing guests. Today, invitations are often much more casual, but the traditional format has survived. Still, there is one important detail many people misunderstand: you are not necessarily required to use the “M” at all.