Air mass is an air mass under certain conditions of temperature, humidity and pressure. The air masses may be hot or cold. Hot ones generally move from tropical regions, and cold ones originate from the polar regions.
Air masses can be parked at a particular location for days and even weeks. But when they move, they cause change in the weather, with clashes between hot and cold air masses: as one advances, the other retreats.
The meeting between two air masses of different temperatures gives rise to a front, ie to a transition area between two air masses. The front can be cold or hot. An cold front It occurs when a cold air mass encounters and pushes a hot air mass, causing fog, rain and a drop in temperature.
Is hot front This occurs when a hot air mass encounters a cold air mass that was parked over a region, causing the temperature to rise.