Hubble's constant

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A ratio used in Hubble's law to express the rate of apparent expansion of the universe, equal to the velocity at which a typical galaxy is receding from Earth divided by its distance from Earth, approximately 71 kilometers per second per megaparsec.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun singular only Alternative spelling of Hubble constant.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (cosmology) the ratio of the speed of recession of a galaxy (due to the expansion of the universe) to its distance from the observer; the Hubble constant is not actually a constant, but is regarded as measuring the expansion rate today