A jet or jet stream is a very fast current of wind found high in the atmosphere of some planets including our own.

A jet usually is a westerly wind, flowing from the west to the east, its path typically meandering. It’s very much like a river or an ocean current, often as fast as 230 miles (370 km) per hour, starting as one stream, stopping, splitting into two or more parts, combining into one stream, or flowing in various directions even including the reverse of the general direction of the main jet.

The main jets are located between the troposphere and the stratosphere, or what is called the tropopause. The strongest though lower jets, called polar jets, are those near the north and south poles. The somewhat weaker but higher jets, called subtropical jets, are those nearer the equator.

If you want to easily remember what a jet is, simply think of it as a pilot’s aid: Jets were first discovered by World War II pilots who found struggled with flying because of these high winds. Now a jet pilot knows to go with instead of against a jet to travel faster and much more smoothly over the ground.