It is a hollow place in the ground, especially a natural underground space large enough for a human to enter.
1 cave. noun \ˈkāv\. Tweet. : a large hole that was formed by natural processes in the side of a cliff or hill or under the ground. 1. : a natural chamber or series of chambers in the earth or in the side of a hill or cliff. 2. cave. n. 1. A hollow or natural passage under or into the earth, especially one with an opening to the surface. 2. A storage cellar, especially for wine. v. caved, cav·ing, caves. v. tr. 1. To dig or hollow out. Rock material produced by the collapse of the ceiling or walls of a cave is called breakdown and may range in size from plates and chips to massive blocks. Most breakdown present in caves today appears to have occurred thousands of years ago. It is generally associated with the early history of cave development. A large cave in southwestern Virginia is used as a natural tunnel by the Southern Railway. From the early 19th century through the Civil War, caves in Kentucky, Tennessee, Virginia, West Virginia, Alabama, Georgia, Arkansas, and Missouri were important sources of nitrates, an essential ingredient of gun powder. cave. A hollow or natural passage under the earth or in the side of a hill or mountain with an opening to the surface. Caves can form in many ways, but especially from the dissolving of limestone. a small group of politicians who break away from the main party; a splinter party. A cave or cavern is a hollow place in the ground, especially a natural underground space large enough for a human to enter. Caves form naturally by the weathering of rock and often extend deep underground. The word cave can also refer to much smaller openings such as sea caves, rock shelters, and grottos. Speleology is the science of exploration and study of all aspects of caves and the cave environment.
http://www.merriam-webster.com/dictionary/cave http://www.thefreedictionary.com/cave http://www.nature.nps.gov/geology/usgsnps/cave/cave.html http://www.nature.nps.gov/geology/usgsnps/cave/cave.html http://www.thefreedictionary.com/cave https://en.wikipedia.org/wiki/Cave
what is a cave