A rigid body is a concept in physics that refers to an idealized object that does not deform under the influence of external forces. In other words, it maintains its shape and size regardless of the forces acting upon it.

Key characteristics of a rigid body include:

1. Fixed Shape: A rigid body does not change its shape when subjected to external forces.

2. Fixed Size: The distance between any two points on a rigid body remains constant.

3. No Deformation: There is no stretching, compression, bending, or twisting of the body under the influence of forces.