Meaning

noun (communication theory) a numerical measure of the uncertainty of an outcome

noun (thermodynamics) a thermodynamic quantity representing the amount of energy in a system that is no longer available for doing mechanical work

originFirst attested in 1867, as the translation of German Entropie, coined in 1865 by Rudolph Clausius in analogy to Energie (“energy”), replacing the root of Ancient Greek ἔργον (érgon, “work”) by Ancient Greek τροπή (tropḗ, “transformation”)).

Etymology from Wiktionary, CC BY-SA 3.0