The Oort Cloud (aka Öpik-Oort Cloud) is a cloud of Minor Planets and Comets at a distance from around 2,000 to possibly 200,000 Astronomical Unit from the Sun. It is the source of Long Period Comets, those with an extremely elliptical orbit and a distant Aphelion (the orbit's far point of the Sun) in the above-given range, and orbiting on random planes rather than somewhat near the Ecliptic. These comets are thought to generally remain at a distance and assume these orbits only when disturbed.
The Oort cloud concept grew from a need to explain the Orbital Inclination of these comets, the fact that the orbits appear unstable, i.e., incapable of lasting billions of years, and that such comet bodies would not survive the repeated sweeps nearing the Sun.
Kuiper Belt (K Belt)