Patches of dense gas and dust in space, usually about 10,000 times more massive than the Sun, from which stars are believed to form. Particles in the cloud are attracted to each other, causing them to form smaller, rotating bodies, which may become stars.
Adapted from "interstellar clouds." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 24 Nov. 2015 <http://www.encyclopedia.com>.