What is the term for the boundary between two different air masses?

The term for the boundary between two different air masses is known as a front. Fronts are significant features in meteorology because they mark transitions between different temperature, moisture, and wind characteristics inherent to the air masses they separate. For instance, a warm front represents the boundary where a warm air mass is replacing a cooler air mass, while a cold front does the opposite.

Understanding fronts is crucial for predicting weather patterns and phenomena, as they often bring about changes in weather conditions such as precipitation, clouds, and shifting winds. Weather fronts can also spawn various types of severe weather, making them central to meteorological studies and forecasting.

While the other terms listed may relate to air pressure or atmospheric behavior, they do not specifically refer to the distinct boundary between two air masses like a front does. Thus, the clarity and definition of the term "front" make it the appropriate choice in this context.