Spectral type is a classification system used in astronomy to categorize stars based on their temperature and the characteristics of their light. This system divides stars into several classes, labeled from O (the hottest) to M (the coolest), with each class further divided into subclasses. The classification is determined by analyzing the star's spectrum, which reveals the presence of various elements and molecules. The spectral type helps astronomers understand a star's properties, such as its age, size, and potential for hosting planets. For example, O-type stars are massive and short-lived, while M-type stars are smaller and can live for billions of years.