jet stream

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

• noun A high-speed, meandering wind current, generally moving from a westerly direction at speeds often exceeding 400 kilometers (250 miles) per hour at altitudes of 10 to 15 kilometers (6 to 9 miles).
• noun A high-speed stream; a jet.

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

• noun meteorology any of the high-speed, high-altitude air currents that circle the Earth in a westerly direction

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

• noun a high-speed high-altitude airstream blowing from west to east near the top of the troposphere; has important effects of the formation of weather fronts