The electronvolt (eV) is a unit of energy.
A gamma scan revealed that the Crystalline Entity left behind a trail of antiprotons with a sharp spike at 10 keV. (TNG: "Silicon Avatar")
The tertiary subspace manifold, the home of a species of solanogen-based lifeforms, was located at a subspace energy level of 16.2 keV. (TNG: "Schisms")