A conserved physical quantity associated with the rotation of an object.
In classical physics, the contribution of each part of a body to the body’s total angular momentum is the part’s mass times its distance from the axis of rotation, times the part’s speed component which points in the direction of rotation and is perpendicular to the axis of rotation.
More information can be found in the spotlight text What figure-skaters, planets, and neutron stars have in common.
In the context of general relativity, angular momentum is an interesting quantity in the physics of black holes. More information about this can be found in the spotlight text How many kinds of black holes are there?