A pediment is a very gently sloping (.5°-7°) inclined bedrock surface. It typically slopes down from the base of a steeper retreating desert cliff, or escarpment, but may continue to exist after the mountain has eroded away.

It is caused mainly by fluvial erosion.

It is typically a concave surface gently sloping away from mountainous desert areas.

Coalescence of pediments over a large area results in a pediplain. Pediplain is an extensive plain formed by the coalescence of pediments. The processes through which pediplains forms is known as pediplanation.

What is a Peneplain?

A peneplain is a low-relief non-constructional plain. The term is also used to imply the representation of a near-final (or penultimate) stage of fluvial erosion during times of extended tectonic stability.

These are flat plains, covered or flooded by river/stream waters over its major part and have no stand-out features like inselbergs or pediments or any other remnants of other stand-out landforms. The plain is simple and flat.