en|tro|py

en|tro|py «EHN truh pee», noun.

1. Physics. a) a measure of the unavailability of energy for conversion into mechanical work in a thermodynamic system, due to the random motion of the molecules which comprise the system. It is directly proportional to the quantity of heat in a body and inversely proportional to its absolute temperature. It vanishes at absolute zero. b) a measure of the degree of disorder of a system. The total entropy of an isolated system cannot decrease with change. It can only remain constant, in a reversible process; or increase, in an irreversible process. The entropy of the universe is increasing. An increase in entropy with change signifies a reduced amount of available energy.

2. Communication and Electronics. the measure of the unpredictability, or unexpectedness, in a message source in a signal system; specifically, the average number of choices a message source has in producing information, measured in bits (binary digits) per symbol, per unit of time, or per message.

╂[< German Entropie, probably influenced by Greek entropíā, entrop a turning in < en- in + trop a turning < trépein to turn]