A star whose state of evolution resembles that of the Sun. The term “dwarf star” derives from the early work of Ejnar Hertzsprung and Henry Norris Russell, who distinguished two kinds of stars, large ones called giants (or supergiants) and smaller ones called dwarfs. “Dwarf” is synonymous with “main sequence star” (Morgan-Keenan-Kellman (MKK) luminosity class V, where the luminosity classes are supergiants = I, bright giants = II, giants = III, subgiants = IV, and dwarfs = V), and implies not size but evolutionary condition. Dwarfs are stars that, like the Sun, fuse hydrogen into helium in their cores, the thermonuclear reactions providing energy and support.