A giant star represents a major stage in the lifecycle of a star, occurring when a star exhausts the hydrogen fuel in its core. As the star’s core contracts and heats up, the overlying layers of gas undergo helium fusion and subsequent shell burning, causing the stellar envelope to expand dramatically. Due to this expansion, the star's radius increases significantly, leading to immense luminosity, while its surface temperature can drop, often shifting its spectral classification toward the red end of the spectrum. The specific path and eventual fate of a giant star are determined primarily by its initial mass; higher mass stars typically traverse the giant phase more rapidly and experience more extreme evolutionary changes than those of lower mass.