Layering
Building a composition from distinct planes at different distances, so the eye moves through the frame from near to far.
In depth
Layering is the more sophisticated form of foreground interest: rather than one near element, the picture has three or four readable depths, each partially overlapping the next. It is the defining technique of much street and documentary photography, where several separate events are stacked in one frame without confusing each other.
Examples in practice
A street photograph with a figure at two metres, a doorway at six and a passing bus at fifteen gives three readable layers.