escape velocity

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

• noun The minimum velocity that a body must attain to escape a gravitational field completely.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Physics) The minimum velocity at which an object must be moving in order for it to overcome the gravitational attraction of a massive celestial body, such as the earth or the sun, and escape beyond its gravitational field into free space. The velocity is calculated as though attained instantaneously at the surface of the celestial body, and is pointed directly away from its center, and neglecting effects of atmospheric friction. Rockets, which accelerate gradually and are moving rapidly at a high altitude when their fuel is exhausted or their engines shut off, may escape even if moving slightly slower at that point than the surface escape velocity. Compare orbital velocity.

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

• noun astrophysics The minimum velocity needed to escape the gravitational field of a planet or other body.

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

• noun the minimum velocity needed to escape a gravitational field