Definitions for jet stream
Random House Webster's College Dictionary
strong, generally westerly winds concentrated in a relatively narrow and shallow stream in the upper troposphere of the earth.
the exhaust of a jet or rocket engine.
Category: Aeronautics, Rocketry
Origin of jet stream:
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
any of the high-speed, high-altitude air currents that circle the Earth in a westerly direction