An FK Comae Berenices star, named after the prototype, is a fast-spinning giant star of spectral type G or K (about as warm or slightly cooler than the Sun but much larger) whose light variations have the same period as the rotation – typically a few days. Changes in brightness of a few tenths of a magnitude are caused by a surface that is more luminous in some areas than others.

FK Com stars may represent a late stage in the evolution of common-envelope stars at which the stellar cores have coalesced.