Dwarf galaxies are small galaxies that contain a relatively low number of stars, typically ranging from a few million to a few billion. They are much less massive than larger galaxies like the Milky Way and often have irregular shapes. Dwarf galaxies can be found in groups or clusters, and they play a significant role in understanding the formation and evolution of the universe. These galaxies are often categorized into different types, including dwarf elliptical, dwarf irregular, and dwarf spheroidal galaxies. Dwarf galaxies are important for studying dark matter, as their gravitational effects can provide insights into this mysterious substance that makes up a large portion of the universe's mass.