Question

define jet stream and gust front

Answer 1

A gust front is the leading edge of cool air rushing down and out from a thunderstorm. There are two main reasons why the air flows out of some thunderstoms so rapidly. 

Jet Stream :
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.

Answer 2

Jet stream: a narrow variable band of very strong predominantle westerly air current encircling the globe several miles above the earth.
Gust storm: an out flow boundary, also known as a gust front, is a storm scale seperating thunderstorm-cooled air from the surrounding air.