1. (planation surface) Gently undulating land surface that cuts indiscriminately across underlying geologic structures and that is the end-product of a long period of erosion. Different types are produced under different environments. Among the more important are the peneplain (humid temperate), etchplain (humid tropical) and pediplain (semi-arid). Marine processes may also cut a marine erosion surface.

2. An irregular surface cut into rock or sediment by the eroding action of flowing water, ice, or by the wind.