An front is a body of air while an air mass is the boundary between two fronts.

An air mass is a large body of air, but a front is the boundary between two air masses

There isn't a difference. Both fronts and air masses are bodies of air.

Over water and moving inland.

Around locations with severe weather.

At high altitudes and descending toward Earth’s surface.

At boundaries between air masses.

Dry, Cold

Humid, Cold

Humid, Warm

Dry, Warm