A mountain is a large landform that stretches above the surrounding land in a limited area usually in the form of a peak. A mountain is generally steeper than a hill. The adjective montane is used to describe mountainous areas and things associated with them. The study of mountains is called Orography. Exogeology deals with planetary mountains, which in that branch of science are usually called montes (singularﾗmons). The highest mountain on Earth based from sea level is Mount Everest (8,848 m (29,029 ft)) in the Himalayas of Asia. The highest known mountain in the Solar System is Olympus Mons on the planet Mars at 21,171 m (69,459 ft).

There is no universally accepted definition of a mountain. Elevation, volume, relief, steepness, spacing and continuity have been used as criteria for defining a mountain. In the Oxford English Dictionary a mountain is defined as "a natural elevation of the earth surface rising more or less abruptly from the surrounding level and attaining an altitude which, relatively to the adjacent elevation, is impressive or notable."