The Kuiper (ky'pur) belt is like a asteroid belt excepted that it is around the the solar system! Since Pluto is the farthest planet from the sun, it's closest to the Kuiper belt. That's how some of the rocks got the nickname "little Plutos."
The Kuiper belt was named after Gerald Kuiper, the man who first man to guess about the existence of Kuiper belt. I say guessed because, in those days, he could not see if he was correct.
This was a idea for 40 years until 1992, when a large object was discovered in part of the solar system where Gerald had said the Kuiper belt was. Several other objects were found quickly and the idea became a part of the solar system !