A "spectral type" is a classification system used in astronomy to categorize stars based on their temperature and the characteristics of their light. This classification is determined by analyzing the star's spectrum, which is the range of colors produced when light is split. The main spectral types are designated by letters: O, B, A, F, G, K, and M, with O being the hottest and M the coolest. Each spectral type is further divided into subclasses using numbers, allowing for more precise categorization. For example, a star classified as G2 is hotter than a G3 star but cooler than a G1 star. This system helps astronomers understand the properties and life cycles of different stars in the universe.