A hill is a landform that extends above the surrounding terrain, in a limited area. Hills often have a distinct summit, although in areas with scarp/dip topography a hill may refer to a particular section of scarp slope without a well-defined summit (e.g. Box Hill). A hillock is a small hill.

Terminology

The distinction between a hill and a mountain is unclear and largely subjective, but a hill is generally somewhat lower and less steep than a mountain. In the United Kingdom 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 . This has led to Cavanal Hill in Poteau, Oklahoma, receive billing as the "World's Tallest Hill" due to its height of . 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.

Artificial hills may be referred to by a variety of technical names. See mound and tumulus.

Areas that would otherwise have hills do not because of glacier cover during the Ice Age. The contrast between the extreme plains of northern Indiana, and the extreme hilliness of southern Indiana is a result of this.

There are various specific names used to describe particular types of hill, based on appearance and method of formation. Many such names originated in one geographical region to describe a type of hill formation peculiar to that region, though the names are often adopted by geologists and used in a wider geographical context. These include:

• Drumlin – an elongated whale-shaped hill formed by glacial action.
• Butte – an isolated hill with steep sides and a small flat top, formed by weathering.
• Tor – a rock formation found on a hilltop; also used to refer to the hill itself, especially in South West England.
• Puy – used especially in the Auvergne, France, to describe a conical volcanic hill.
• Pingo – a mound of earth-covered ice found in the Arctic and Antarctica.

Historical significance

Many settlements were originally built on hills, either to avoid or curb floods, particularly if they were near a large body of water, or for defence, since they offer a good view of the surrounding land and require would-be attackers to fight uphill. For example, Ancient Rome was built on seven hills, protecting it from invaders.