An Oort Cloud is a very expansive spherical shell, located in the far system, around most stars or star systems, consisting of numerous small bodies of cometary material.
A typical Oort cloud lies between 0.5 and 1 light-years from its primary star and has an aggregate mass generally equivalent to that of Terra, a large world; density is thus extremely low.
An overview of the Terra system, representative of the structure of a star system and the position of the Oort Cloud.
History & Background (Dossier)
The Oort cloud is named after its discoverer, Terran astronomer Jan Oort.
The main constituents of cometary bodies are ice and dust ("dirty snowballs").
Bodies in the Oort cloud are occasionally perturbed by collisions or by the influence of nearby stars into orbits which pass near the star; these form the visible comets.
References & Contributors (Sources)