moun·tain

Abbr. Mt. or Mtn. A natural elevation of the earth's surface having considerable mass, generally steep sides, and a height greater than that of a hill.

From http://dictionary.reference.com/

Mountains are landforms that rise above the land surface in a limited area. They usually have steep, sloping sides and slightly rounded or sharp ridges and peaks. A mountain generally has a height of over 600 meters above the land, and exists on every continent and under the oceans. There are also different types of mountains: fold, block, volcanoes, dome and plateau.

Mountains are also more than just landforms, as humans depend much on them for survival. A tenth of the world’s population, approximately 60 million, lives near or on the mountains. They’re also a source of precious freshwater: all major rivers are fed by tributaries from mountain sources. Mountains appear in over 75 percent of the world’s countries, and cover one-fifth of Earth’s land surface.

Suffice to say, mountains are very important to the survival and livelihoods of humans. Click on the links on the left to find out more about them.