Someone with a US Chess Federation rating between 2200 and 2399.

A player whose Elo rating is 2200 or higher. If the player's rating drops below 2200 the title is revoked.

Loosely, a strong chess player who would be expected to beat most amateurs. It may also refer to a formal title such as International Master or National Master. Standards vary, but a master will usually have an Elo rating of over 2200.