Why is the boundary between two air masses called a front

The boundary between two air masses with different temperatures and different property is called front.

Explanation:

The boundary between two air masses is regarded as a weather front. Weather fronts can be either warm or cold fronts. The characteristics either side of a front would display the characteristics you’ve listed. So typically, if you considered an air mass ahead of a warm front which could be a polar maritime, this would be cold air so would have high density, and because it’s cold it’s ability to hold water (humidity) would be low. Conversely the air mass behind the warm front could be a tropical maritime air mass. So it would be warm, less dense and very humid.

yes it is weird but true