Oort cloud: Meaning and Definition of

Oort' cloud"

Pronunciation: (ôrt, ōrt), [key]
— Astron. Astron.
  1. a region of the solar system far beyond the orbit of Pluto in which billions of comets move in nearly circular orbits unless one is pulled into a highly eccentric elliptical orbit by a passing star.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.