From AMS Glossary
The leading edge of a mesoscale pressure dome separating the outflow air in a convective storm from the environmental air.
This boundary, which is marked by upward motion along it and downward motion behind it, is followed by a surge of gusty winds on or near the ground. A gust front is often associated with a pressure jump, wind shift, temperature drop, and sometimes with heavy precipitation. Gust fronts are often marked by arcus clouds.