An early-type star, also known as a young or hot star, is a term used to describe a type of star that is relatively young and has a high surface temperature. Some synonyms for the term include O-type star, B-type star, and A-type star. O-type stars are the hottest and most massive stars, while A-type stars are less massive and slightly cooler. B-type stars are intermediate between O and A type stars in terms of temperature and mass. Other synonyms for early-type stars include main-sequence stars and blue giants. These stars are important in understanding the evolution of galaxies and the formation of new stars.