1. for a closed thermodynamic system, a quantitative measure of the amount of thermal energy not available to do work.
2. A measure of the disorder or randomness in a closed system.
3. A measure of the loss of information in a transmitted message.
4. the tendency for all matter and energy in the universe to evolve toward a state of inert uniformity.
5. inevitable and steady deterioration of a system or society.

1. A measure of the amount of information and noise present in a signal. originally a tongue in cheek coinage, has fallen into disuse to avoid confusion with thermodynamic entropy.
2. the tendency of a system that is left to itself to descend into chaos.

1. 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.

1. in physics: as used by Clausius, the inventor of the word, and others, that part of the energy of a system which cannot be converted into mechanical work without communication of heat to some other body, or change of volume.
2. as used by tait and others, the available energy; that part of the energy which is not included under the entropy in sense .

1. (communication theory) a numerical measure of the uncertainty of an outcome
2. (thermodynamics) a thermodynamic quantity representing the amount of energy in a system that is no longer available for doing mechanical work