Meaning of jet stream

jet' stream"

Pronunciation: [key]
  1. strong, generally westerly winds concentrated in a relatively narrow and shallow stream in the upper troposphere of the earth.
  2. similar strong winds in the atmosphere of another planet: jet streams on Jupiter.
  3. the exhaust of a jet or rocket engine.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.