The story
Coined by American cosmologist Michael Turner in 1998, in reference to the earlier term dark matter.
Etymology from Wiktionary, CC BY-SA 4.0.
dark energy
Today it means: A hypothetical form of energy thought to be spread uniformly throughout space (and time) and to have anti-gravitational properties: it represents a possible mechanism for the cosmological constant, and thus is one of the possible explanations for the current accelerating rate of expansion of the universe; and it is estimated to account for about 74% of the mass-energy of the universe. Full definition →