Definition of "entropy" []

• For a closed thermodynamic system, a quantitative measure of the amount of thermal energy not available to do work. (noun)
• A measure of the disorder or randomness in a closed system. (noun)
• A measure of the loss of information in a transmitted message. (noun)
• The tendency for all matter and energy in the universe to evolve toward a state of inert uniformity. (noun)
• Inevitable and steady deterioration of a system or society. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "A typical rebuttal is to suggest that information entropy and thermodynamic entropy are unconnected, citing the apocryphal story that Shannon picked the term entropy because “nobody understands what it means”."
• "In Über die bewegende Kraft der Wärme (1865) he introduced the term entropy, stating that the entropy of the universe tends to increase."
• "Rudolf J.E. Clausius also introduced (1850) a quantitative measure of irreversibility which he termed entropy, and he posited the so-called second law of thermodynamics by which for a closed physical system the total entropy of the system cannot decrease in time but only increase or at most remain constant."