A sudden, transitory burst of activity in the Sun's atmosphere involving the release of radiation and high-energy particles: The origin of flares is uncertain, although they seem to be related to areas of high magnetic fields.

A star whose brightness can increase by as much as two to 100 times in a matter of minutes, then return to normal: The sudden brightness of a flare star, as a faint red dwarf, fades away quickly after amounting to many magnitudes of bright intensity.