What describes inelastic collisions?

Inelastic collisions are characterized by the fact that they do not conserve kinetic energy. During these types of collisions, some of the initial kinetic energy of the colliding objects is transformed into other forms of energy, such as thermal energy or sound energy, and thus is not retained as kinetic energy after the collision.

Though momentum is conserved in all types of collisions (including elastic and inelastic), the key feature of an inelastic collision is the loss of kinetic energy. This energy transformation results in the two bodies often sticking together or deforming when they collide, which further demonstrates how kinetic energy is not conserved.

In summary, inelastic collisions uniquely differentiate themselves from elastic collisions through the loss of kinetic energy, which aligns with the correct choice provided.