what is elastic collision?

Answer 1

In an elastic collision the total kinetic energy of the system after the collision is equal to the total kinetic energy of the system before the collision. If your next question si going to be what is Total Kinetic Energy, it is defined as energy of motion.

A collage level lab showing this concepts if located at the following link:
http://www2.truman.edu/~mgoggin/labs/Collisions.pdf

Answer 2

A collision between 2 objects where no energy is lost. Think of a superball. When you drop it, it bounces a little lower each time. Some of the kinetic energy is converted to sound, some to heat, and some is transferred to whatever you are bouncing it against. In an elastic collision, the ball would keep bouncing at the origignal height forever, because no energy would be lost in the collision. Contrast the example I gave with a totally inelastic collision, such as a ball of wet toilet paper hitting the ground. No bounce back because all the energy is spent in the sound and deforming the ball of paper once it hits.

Answer 3

It means the total energy and momentum before and after the collision remain the same. No energy is converted to heat when the collision takes place.