The simple definition for anchored in backgammon would be that a player has two or more checkers on the opponent's inner board. It is a well-known strategy to start a game with an anchor on the opponent's 1-point.

The term is sometimes used as advanced anchor, with a slight change in meaning, basically because an advanced anchor is a better position than a simple anchor. In this case it is a made point higher in the opponent's board than the 24 point. An advanced anchor is good because the player has more chances to attack the opponent's checkers, and also he can escape his own checkers easier.