The story
Named after physicist James Clerk Maxwell (1831–1879) and demon, and probably from Greek daemon, a mythological being intermediate between gods and men.
Etymology from Wiktionary, CC BY-SA 4.0.
Maxwell's demon
Today it means: A hypothetical creature in a thought experiment. Maxwell’s demon, if it existed, would act as a sort of gate guard by sorting between higher-energy molecules and lower-energy molecules within an enclosed space. Because such a sorting process would tend to decrease entropy, it would violate the second law of thermodynamics. Full definition →