What defines a depression in landform terminology?

A depression in landform terminology is characterized by a concave shape. This means that the landform is lower than the surrounding areas, creating a basin or hollow. Depressions can be found in various forms, such as valleys, sinkholes, or craters, and are identified by their inward-sloping features, which distinguish them from elevated landforms or flat terrains.

In the context of landforms, options such as a flat area with no elevation or an elevated area above sea level do not accurately describe a depression, as they do not imply a concave structure. Similarly, a landform that slopes outward suggests a convex shape, which is the opposite of what defines a depression. Thus, the defining characteristic of a depression lies in its concave landform, making it unique and identifiable within the landscape.