Giant Star
A member of a broad category of stars that have luminosities between 10 and 1000 times that of the Sun, and radii typically between 10 and 100 times the Sun's. A star becomes a giant when the hydrogen fuel available for nuclear fusion reactions in its core is depleted and the adjustment to the new energy balance causes the outer layers to expand greatly. The surface temperature drops, but the total luminosity rises because of the great increase in surface area. (Mitton, 1993, Dictionary of Astronomy, London: Penguin Books)