Inelastic collision (or inelastic scattering):

If the sum of the kinetic energies of the colliding bodies or particles after collision is not the same as the sum of the kinetic energies of that colliding bodies or particles before collision, then this type of collision is said to be inelastic collision. Most type of collisions which occur in nature are inelastic collision.

A collision is said to be perfectly inelastic if the colliding bodies stick together on collision and the loss of the kinetic energy is maximum, consistent with the law of conservation of momentum.