Definitions for "Red supergiant"
A relatively old star whose diameter is about 100 times bigger than it was originally, and had become cooler (the surface temperature is under 6,500 K). They are frequently orange-red in color. Betelgeuse is a red supergiant.
An extremely luminous red star. Often found on the asymptotic giant branch of the H-R diagram.
An extremely luminous and large red star.