Matter, particle and body:
Matter is anything which occupies space, possesses mass provides resistance to any stress, example Iron, air, stone, Water.
A body of negligible dimension is called as particle. But particle has mass. A body consists of Number of particle, It has definite shape.
A rigid body can be defined as the combination of a large number of particles, which occupy fixed position with respect to the other, both before and after applying load. Or, A rigid body can be defined as body, which can retain its shape and size even if subjected to some external forces. In reaklity, nobody is perfectly rigid. But for sake of simplicity, we take the bodies as rigid bodies.
An elastic body is that that regain its original shape after removal of the external loads.
The basic difference between rigid body and an elastic body is that rigid body do not change its shape and size before and after application of force, while an elastic body can change its shape and size after application of load, and again regain its shape after removal of external loads.