It is the angle made by a body while moving in a circular path. Before we go any further into the topic, we have to understand what is meant by rotational motion. When a rigid body is rotating about its own axis, the motion ceases to become a particle. It is so because in a circular path velocity and acceleration can change at any time. The rotation of rigid bodies or bodies which will remain constant throughout the duration of rotation, over a fixed axis is called rotational motion.

The angle made by the body from its point of rest at any point in the rotational motion is the angular displacement.

Angular acceleration is measured in units of angle per unit time squared (which in SI units is radians per second squared), and is usually represented by the symbol alpha (α). In two dimensions, angular acceleration is a pseudoscalar whose sign is taken to be positive if the angular speed increases counterclockwise or decreases clockwise, and is taken to be negative if the angular speed increases clockwise or decreases counterclockwise. In three dimensions, angular acceleration is a pseudovector.