Masons are a group, usually all on the Pro-Town side, that know each other to be innocent. They can communicate with each other at Night, if they choose, but otherwise usually have no special abilities.
In one variation of the Mason role, the Masons cannot reveal that they are Masons to the town through roleclaiming. Instead, they must find other ways to defend each other.
Recently it has become possible to have a Mason who is also Scum. This creates a "game-within-a-game" scenario where the Masons have to discern whether or not they can trust each other.
See also Cults.