Question

What are Jet streams?

Answer 1

Here's you're Answer--

Jet streams are fast flowing, narrow, meandering air currents in the atmospheres of some planets, including Earth. On Earth, the main jet streams are located near the altitude of the tropopause and are westerly winds. 

Answer 2

A narrow group of strong westerly winds several miles above sea level. there are around three jet streams in northern and southern hemisphere.