Citation:
External torque refers to the rotational force applied to an object by an external agent, causing it to rotate around a fixed axis. It is the net torque acting on an object due to forces external to the system.
Moment of inertia is a measure of an object's resistance to changes in its rotational motion. It depends on both mass distribution and shape.
Angular acceleration refers to how quickly an object's angular velocity changes over time. It is caused by applying a net torque on the object.
Conservation of angular momentum states that if no external torques act on a rotating system, then its total angular momentum remains constant.