Which planet is known as dwarf planet ?

While digging in the space and astronomy i got to know that planets in our solar system are categorized in many ways and they are not just these 8 planets in the solar system. But there are also some dwarfs planets exist and revolve around the sun. I am curious to know what are these dwarf planets and why they are not categorized as the major planets.
While digging in the space and astronomy i got to know that planets in our solar system are categorized in many ways and they are not just these 8 planets in the solar system. But there are also some dwarfs planets exist and revolve around the sun. I am curious to know what are these dwarf planets and why they are not categorized as the major planets.