Entropy is a measure of the amount of randomness or disorder in a system. In chemical reactions and molecular processes, spontaneous progress is always made in a direction which will increase the total state of disorder; as an analogy, throwing a bundle of confetti in the air will result in many isolated pieces scattered all over the ground, not the single bundle from which the pieces originated.

In another example, the entropy of an unburned piece of wood and its surroundings is lower than the entropy of the ashes, burnt remains, and warmed surroundings due to burning of that piece of wood. For parents, the concept of entropy is easy to understand, because children inevitably increase entropy, while parents struggle to reduce it.