Plain English Meaning
A front is the dividing line where two large bodies of air with different properties meet. Because the air on each side is different, the weather usually changes as the front passes through.
Full Definition
The boundary between two air masses of different temperature, humidity, or density. As one air mass moves and meets another, the transition zone between them is called a front, and weather changes — wind shifts, cloud development, precipitation, and pressure changes — typically occur along this boundary.
Context Anchor
Seen in aviation weather reports, forecasts, weather charts, and preflight weather briefings.