What is entropy?

Entropy:

In simple terms, the measure of the level of disorder in a closed but changing system, a system in which energy can only be transferred in one direction from an ordered state to a disordered state. Higher the entropy, higher the disorder and lower the availability of the system's energy to do useful work. Although the concept of entropy originated in thermodynamics (as the 2nd law) and statistical mechanics, it has found applications myriad of subjects such as communications, economics, information science and technology, linguistics, music. In day-to-day life it manifests in the state of chaos in a household or office when effort is not made to keep things in order.