What defines a front in meteorology?

A front in meteorology is specifically defined as an area of discontinuity between two different air masses. This means that a front marks the boundary where there is a significant difference in temperature, humidity, and density between the air masses involved. These differences are crucial as they lead to various weather phenomena, including precipitation and changes in wind patterns.

When two air masses meet, they do not mix easily due to their differing characteristics, which can lead to the formation of clouds and storms, depending on the stability and moisture content of the air masses. The study of fronts is essential for predicting weather changes and understanding how different air masses interact within the atmosphere.

The other options do not capture the essence of what a front represents in meteorology. Significant altitude changes pertain more to topography rather than the dynamics of air masses. An area with uniform temperature doesn't match the definition of a front, as it lacks the discontinuity necessary to define such boundaries. Similarly, changes in wind direction can occur without the presence of a front, as they may result from other atmospheric phenomena unrelated to the interaction of air masses.