Question

What is a jet stream?

Answer 1

Definition:

Jet streams are relatively narrow bands of strong wind in the upper levels of the atmosphere. The words blow from west to east in jet streams but the flow often shifts to north and south. Jet streams follow the boundaries between hot and cold air. The earth's rotation is responsible for the jet stream as well.

Answer 2

a narrow variable band of very strong predominantly westerly air currents encircling the globe several miles above the earth. There are typically two or three jet streams in each of the northern and southern hemispheres.