Define Kinetic Energy.

Hint: When external work is done by the system, it imparts some energy to the system. This energy can be due to change in position of the particle or due to the change in the speed of the particle. The change in position of the particle is due to the Kinetic Energy. This change in position can be either horizontal or vertical. Energy exists in many forms. Some of them are Kinetic Energy, Potential Energy, Chemical Energy, Nuclear Energy, etc.

Complete step by step answer:
Kinetic Energy is defined as the energy which is produced due to the motion of an object. It depends on the speed of the object as well as the mass of the object which is in motion. Expression for Kinetic energy is expressed as,
$K.E.= \dfrac {1}{2}m{v}^{2}$
Where, m is the mass of the object
               v is the speed of the object
From the above expression it can be inferred that if the velocity of an object doubles, then the Kinetic energy quadruples. S.I. unit of Kinetic energy is Joules (J). Examples of Kinetic energy include falling of water from the waterfall, shooting of rubber bands etc.
The value of Kinetic energy can be either zero or positive. As it is a scalar quantity, direction of the motion of the object does not matter. Environment has a huge impact on the kinetic energy of the object and thus it is relative to the environment.

Note:
Kinetic Energy is different from Potential energy. Potential energy is the energy related to the position of the object. The sum of work done by the forces acting on each particle of a system is equal to the sum of change in kinetic energy of each particle in the system. This is named as the Work-energy Theorem. Kinetic energy can be converted into other forms of energy and transmitted among the objects.