Quiescent galaxies are a type of galaxy that has very low levels of star formation activity, meaning that they are not actively forming new stars. These galaxies are often older and more mature compared to star-forming galaxies. Quiescent galaxies typically have a red color due to the presence of older, redder stars in their populations. They are often found in galaxy clusters, where interactions with other galaxies and environmental influences can quench their star formation. Studying quiescent galaxies can provide important insights into the formation and evolution of galaxies over cosmic time.