1) A cave, especially when large and formed by underground water, or a large chamber in a cave. 2) A natural cavity, chamber or recess which leads beneath the surface of the earth, generally in a horizontal or obliquely inclined direction. It may be in the form of a passage or a gallery, its shape depending in part on the joint pattern or structure of the rock and partly on the type of process involved in its excavation. Thus, caves worn by subterranean rivers may be different in character from, and of considerably greater extent than, a sea-cave eroded by marine waves. 3) A natural underground open space, generally with a connection to the surface and large enough for a person to enter. The most common type of cave is formed in limestone by dissolution.