A rigid body is a system of particles with a finite size that do not get deformed under the influence of any external force. The distance between any two particles of an ideal rigid body does not change even when it is under the influence of external forces.
The motion of a rigid body in which the velocity of all the constituent particles is the same at any instant of time is known as translational motion. The motion of any rolling body is a combination of rotational and translational motions.
The fixed line about which a rigid body rotates is called the axis of rotation. When a rigid body is in rotational motion, every point on it moves along a circular path with its centre on the axis of rotation and the plane of this circle perpendicular to the axis of rotation.
If a rigid body is fixed to an axis or a point, its motion is pure rotational motion. If the rigid body is free, it can have pure translational motion or a combination of translational and rotational motion. The motion in which the axis of rotation is not fixed but the point of contact is fixed is called precession.