A cave is a natural underground void large enough for a human to enter. Some people suggest that the term 'cave' should only apply to cavities that have some part which does not receive daylight; however, in popular usage, the term includes smaller spaces like sea caves, rock shelters and grottos.

Speleology is the science of exploration and study of all aspects of caves. Exploring a cave for recreation or science may be called "caving", "potholing", or occasionally (only in Canada and the United States) "spelunking".