Sit

From WoWWiki

A non-combat position where your character crouches or squats on the ground or a chair, as opposed to standing.

A character cannot engage in combat or use many items or skills directly from a sitting position, they must first stand. Jumping, walking, or running from a sitting position will cause a character to immediately stand and take the appropriate action.

Melee attacks against a sitting target automatically hit and cause double damage. The first damage taken while sitting will cause a target to immediately stand. The double damage registers as a critical hit in the combat log, but does not trigger abilities as a normal crit would (such as the Fury Warrior talent: Enrage)

Sitting while in combat immediately stops auto-attacks, but not spell-casting.

It takes a short amount of time to sit from a standing position and about equal amount of time to stand from a sitting position. Some benches or chairs can be right-clicked to put the character into a sitting position on the bench or chair.

All normal eating of food and drinking of drinks requires sitting and the character will automatically try to sit when trying to eat or drink (except for drinking potions).

Your natural healing rate is increased when sitting.

As of Patch 2.3, if you are seated and try to use abilities that require you to be standing, you will stand up and use them. This can be disabled with: /console autoStand 0