Spectral type refers to the categorization of stars based on their spectral characteristics. Some common synonyms for spectral type include spectral class, stellar classification, and spectral category. These terms are often used interchangeably in astronomy and astrophysics. Spectral type is assigned based on the star's temperature, and it ranges from O-type (hottest) to M-type (coolest). This classification system is important because it provides information about a star's size, mass, and luminosity. Other related terms include absorption lines, which are used to determine a star's spectral type, and Hertzsprung-Russell diagram, which is a plot of a star's luminosity versus temperature and helps to classify stars according to their spectral type.