Mas is the title of a religious leader on the planet Edema. The Mas is the head of the Edemian faith, and is considered the personal emissary of the Edemian god K'olkr.
In addition to his role as a religious leader, the Mas is also the head of the Edemian military forces, and has Edemian Holy War vessels available to carry out his wishes.
In 2369, Marko was the Edemian who held the title of Mas. (DS9 novel: The Siege)