Closed Guard

From OTMWiki

The closed guard is the typical guard position. The legs are hooked behind the back of the opponent, preventing him or her from standing up or moving away. The opponent needs to open the legs up to be able to improve positioning. The bottom combatant might transition between the open and closed guard, as the open guard allows for better movement, but also increased risk in the opponent passing the guard.

The closed guard is the position that BJJ is best known for due to the success Royce Gracie experienced in the early days of the UFC. The closed guard in very effective in BJJ for keeping an opponent in a position where you can work your submissions. In MMA it served Royce Gracie well to keep his much larger opponents from inflicting too much damage.