Elastic bodies: The bodies which rebound after impact are called elastic bodies.
The impact between two rubber spheres is an elastic impact.

Inelastic bodies: The bodies which does not rebound at all after its impact are called inelastic bodies.
The impact between two lead spheres or two clay spheres is approximately an inelastic impact.

Coefficient of restitution is defined as the ratio of Relative velocity after impact to Relative velocity before impact. Coefficient of restitution is denoted by 'e'.
e = 0, For perfectly inelastic bodies .
e = 1, For perfectly elastic bodies.
0>e>1,(value of e lies between zero and one) For bodies neither perfectly inelastic nor perfectly elastic.