Entropy

n. measure of the level of disorder in a system; amount of unavailable energy in a system (Thermodynamics)

For other uses, see: information entropy (in information theory) and entropy (disambiguation). In physics, entropy, symbolized by S,( from the Greek μετατροπή (metatropi) meaning "transformation"), is a measure of the unavailability of a  system’s energy to do work. Entropy is central to the second law of thermodynamics and the combined law of thermodynamics, which deal with physical processes and whether they occur spontaneously. Spontaneous changes, in isolated systems, occur with an increase in entropy. Spontaneous changes tend to smooth out differences in temperature, pressure, density, and chemical potential that may exist in a system, and entropy is thus a measure of how far this smoothing-out process has progressed. In short Entropy is a function of a quantity of heat which shows the possibility of conversion of that heat into work. The increase in entropy is small when heat is added at high temperature and is greater when heat is added at lower temperature. Thus for maximum entropy there is minium availability for conversion into work and for minimum entropy there is maximum avilability for conversin into work.
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Entropy /en·tro·py/ 1. the measure of that part of the heat or energy of a system not available to perform work; it increases in all natural [more]Entropy - Community and Resources

Noun
1. (communication theory) a numerical measure of the uncertainty of an outcome; "the signal contained thousands of bits of information"
(synonym) information, selective information
(hypernym) information measure
(classification) communications, communication theory
2. (thermodynamics) a thermodynamic quantity representing the amount of energy in a system that is no longer available for doing mechanical work; "entropy increases as matter and energy in the universe degrade to an ultimate state of inert uniformity"
(synonym) randomness, S
(hypernym) physical property
(hyponym) conformational entropy
(classification) thermodynamics

(n.)
A certain property of a body, expressed as a measurable quantity, such that when there is no communication of heat the quantity remains constant, but when heat enters or leaves the body the quantity increases or diminishes. If a small amount, h, of heat enters the body when its temperature is t in the thermodynamic scale the entropy of the body is increased by h / t. The entropy is regarded as measured from some standard temperature and pressure. Sometimes called the thermodynamic function.