A hill is a landform that extends above the surrounding terrain. It often has a distinct summit. Terminology The distinction between a hill and a mountain is unclear and largely subjective, but a hill is universally considered to be not as tall, or as steep as a mountain. Geographers historically regarded mountains as hills greater than above sea level, which formed the basis of the plot of the 1995 film The Englishman who Went up a Hill but Came down a Mountain. In contrast, hillwalkers have tended to regard mountains as peaks above sea level. The Oxford English Dictionary also suggests a limit of and Whittow states "Some authorities regard eminences above as mountains, those below being referred to as hills." Today, a mountain is usually defined in the UK and Ireland as any summit at least high, while the official UK government's definition of a mountain is a summit of or higher. Some definitions include a topographical prominence requirement, typically or . In practice, mountains in Scotland are frequently referred to as "hills" no matter what their height, as reflected in names such as the Cuillin Hills and the Torridon Hills. In Wales, the distinction is more a term of land use and appearance and has nothing to do with height. For a while, the US defined a mountain as being or more tall. Any similar landform lower than this height was considered a hill. The United States Geological Survey, however, has concluded that these terms do not in fact have technical definitions in the US The Great Soviet Encyclopedia defined "hill" as an upland with a relative height up to . A hillock is a small hill. Other words include knoll and (in Scotland, Northern Ireland and northern England) its variant, knowe. Artificial hills may be referred to by a variety of technical names, including mound and tumulus. Hills may form through geomorphic phenomena: faulting, erosion of larger landforms such as mountains and movement and deposition of sediment by glaciers (notably moraines and drumlins or by erosion exposing solid rock which then weathers down into a hill). The rounded peaks of hills results from the diffusive movement of soil and regolith covering the hill, a process known as downhill creep. Various names may be used to describe types of hills, based on appearance and method of formation. Many such names originated in one geographical region to describe a