This is a tag for asteroids, not dwarf planets or any other astronomical object.
Asteroids are minor planets (especially those in the inner solar system). The larger asteroids can be called planetoids. The term asteroid has been applied to any astronomical object orbiting the Sun that did not show the disc of a planet or the characteristics of an active comet. There are millions of asteroids, many thought to be shattered pieces of rock left over from collisions, the formation of our solar system, and planetesimals (bodies within the young Sun's solar nebula that never grew large enough to become planets). Some asteroids can be captured by a planet's gravity and become moons, such as Phobos and Deimos did for Mars. Below are a few pictures of asteroids.
There is more information about asteroids here.