Dwarf spherical galaxies (also referred to as dwarf spheroidal galaxies) are among the smallest and most common type of galaxy. They are extremely small and faint, and only a few have been discovered in Earth's Local Group, but it is likely that most galaxies have several spheroidal companions. Many dwarf spheroidal galaxies resemble globular clusters, and distinguishing the two can be difficult. Most of the Milky Way's and Andromeda (M31)'s companion galaxies are of this type.