A cave or cavern is a natural underground space large enough for a human to enter. The term applies to natural cavities some part of which is in total darkness. The word cave also includes smaller spaces like rock shelter

Rock shelter

A rock shelter is a shallow cave-like opening at the base of a bluff or cliff....

s, sea caves, and grotto

Grotto

A grotto is any type of natural or artificial cave that is associated with modern, historic or prehistoric use by humans. When it is not an artificial garden feature, a grotto is often a small cave near water and often flooded or liable to flood at high tide...

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Speleology

Speleology

Speleology is the scientific study of caves and other karst features, their make-up, structure, physical properties, history, life forms, and the processes by which they form and change over time...

 is the science of exploration and study of all aspects of caves and the environment which surrounds the caves. Exploring a cave for recreation or science may be called caving, potholing, or, in Canada and the United States, spelunking (see caving

Caving

Caving—also occasionally known as spelunking in the United States and potholing in the United Kingdom—is the recreational pastime of exploring wild cave systems...

).
The formation and development of caves is known as speleogenesis

Speleogenesis

Speleogenesis is the origin and development of caves, the primary process that determines essential features of the hydrogeology of karst and guides its evolution...

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