Blazars are a type of active galactic nucleus (AGN) that emit powerful jets of particles and radiation. These jets are directed almost directly toward Earth, making blazars some of the brightest objects in the universe. They are powered by supermassive black holes at the centers of galaxies, which consume surrounding material and release immense energy. The intense light from blazars can vary dramatically over short periods, making them important for studying cosmic phenomena. They are often classified into two main types: BL Lacertae objects and flat-spectrum radio quasars, based on their spectral characteristics and brightness.