Spectral class is a classification system used in astronomy to categorize stars based on their temperatures and the characteristics of their light spectra. The main spectral classes are O, B, A, F, G, K, and M, with O being the hottest and M the coolest. Each class is further divided into subclasses, allowing for a more detailed classification. The spectral class of a star is determined by analyzing its light spectrum, which reveals the presence of various elements and molecules. This information helps astronomers understand a star's temperature, age, and chemical composition, contributing to our knowledge of stellar evolution and the universe.