Foreground, Middleground, Background

Foreground - the parts of a piece that appear closest to the viewer

Middleground - the portion of a piece that appears in the middle, usually seems to be the focus of a piece

Background - the portions of a piece that appear to be furthest from the viewer

Cezanne - Landscape Near Aix, the Plain of the Arc River

In this landscape by Cezanne, the foreground would be the rocks and bushes closest to the viewer. The middle ground would be the trees. The background would be the mountains, hills and the sky.