The Kuiper Belt (aka Edgeworth-Kuiper Belt or K Belt) is a region beyond Neptune (30-50 AU) with Comets and Minor Planets (Asteroid-like or somewhat comet-like). It was hypothesized over time, notably Kenneth Edgeworth in 1943 and Gerard Kuiper in 1951, and was clearly identified in 1992. Since then, over 1000 have been discovered, and estimates are there could be 10,000, totaling 1/25 to 1/10 Earth masses. It includes objects more massive than does the Asteroid Belt.
Unlike the much further distant Oort Cloud, the Kuiper belt is somewhat flat, i.e., close to the Ecliptic. The main part is in the region ranging from 2:3 to 1:2 Orbital Resonance with Neptune (40 to 48 AU), and many have little Eccentricity (unlike Pluto). Others have orbits suggesting scattering, e.g., more eccentric and/or with some Orbital Inclination. Some are in families suggesting a past breakup of a larger body.
Bodies in the Kuiper Belt are known as Kuiper Belt Objects (K Belt Objects, KB Objects, KBOs, Edgeworth-Kuiper Belt Objects or EKBOs). Among the largest:
Those with high eccentricity and/or inclination are sometimes termed Extreme Kuiper Belt Objects, abbreviated EKBO (or eKBO), obviously ambiguous as it also abbreviates Edgeworth Kuiper Belt Object. A Classical Kuiper Belt Object (or Classical KBO or Cubewano) has low eccentricity, is always beyond Neptune (unlike Pluto) and has no orbital resonance with Neptune.