Kinetic energy is the energy which moving objects have. You can think of Kinetic energy as the energy of movement, because it refers to any object that is moving at that present time. This energy can be changed into other sorts of energy such as heat (if something hits with something soft and does not bounce), potential energy (if it is moving upwards and gets higher), or even light (if it is moving very, very fast or if it hits something which sparks like flint or iron/Aluminium). However, heat, light, sound, mechanical energy, electrical, and other types of energy are also types of kinetic energy.
Kinetic Energy is equal to the mass of something times its velocity (or speed) times its velocity again, all times ½: