Rotational Momentum:  Angular momentum is the tendency of an object in rotational movement to continue to rotate in a particular direction in the absence of any interfering force. An object's momentum will not change unless it is acted upon by an outside force. When the object (or a system of objects) is spinning, other factors have to be considered in discussing the momentum of the rotational movement. This momentum is referred to as angular momentum.

Definition provided by Book Rages

Conservation to Rotational Momentum