- ⌂ a saucer-shaped surface depression produced when underlying material, such as limestone or salt, dissolves or when caves, mines, etc. collapse
A natural depression in a land surface communicating with a subterranean passage, generally occurring in limestone regions and formed by solution or by collapse of a cavern roof.
- (geology) A hole formed in soluble rock by the action of water, serving to conduct surface water to an underground passage
- A depressed area in which waste or drainage collects.
- (pinball) A hole in the playfield that rewards the player when the ball is guided into it.
- (Internet) A DNS server that has been configured to hand out non-routeable addresses for all domains, so that every computer that uses it will fail to get access to the real website.