The Oort Cloud is a theoretical, distant region of the solar system that is believed to contain a vast number of icy bodies and comets. It is thought to be a spherical shell surrounding the solar system at a great distance, far beyond the orbit of Pluto and the Kuiper Belt.

Named after the Dutch astronomer Jan Oort, who proposed its existence in 1950, the Oort Cloud is divided into two main parts: the inner Oort Cloud (or Hills Cloud) and the outer Oort Cloud. The inner Oort Cloud is somewhat closer to the solar system and is thought to be more spherical in shape, while the outer Oort Cloud is more distant and possibly more diffuse.

The Oort Cloud is considered the source of long-period comets that enter the inner solar system. These comets are believed to be perturbed by gravitational interactions, possibly with nearby stars or the galactic tide, causing them to be sent towards the Sun. Despite its importance, the Oort Cloud has not been directly observed due to its vast distance and the faintness of its objects. Its existence is inferred from the orbits of comets and the dynamics of the solar system.