Hills (synonyms: hillocks, knolls, hill country, hillsides, bluffs, dunes, highlands; example toponyms: Carne’s Hill, The Northern Highlands) are terrain features that reach a higher elevation than the surrounding landscape. Hills are far smaller than mountains, though hills may be old mountains that have been eroded over time. Hills provide both a defensive advantage to structures built on their summits as well as a greater view of their surroundings. Hills may be the sites of mines, quarries, hillside burrows, windmills, watchtowers, and castles. Towns and cities are often also built on hills to avoid flooding. Farms or terraced farms may be present. In locations where hills are on a coast, the eroding action of the tides may generate sea cliffs, sea caves, and sea stacks. Rivers that flow through hill lands may create canyons and may be more prone to have rapids and waterfalls.

Hills can be difficult terrain to cross.