"Live rock" is rock from the ocean that has been introuced into a saltwater aquarium, which confers to the closed marine system multiple benefits desired by the salt water marine hobbyist. The name sometimes leads to misunderstandings as "live rock" is itself not actually alive, but is made simply from the calcium carbonate skeletons of long dead corals, or other calcareous organisms, which in the ocean form the majority of coral reefs. When taken from the ocean it is usually encrusted with Coralline algae and inhabited by a multitude of marine organisms. The many forms of micro and macroscopic marine life that live on and inside of the rock, and which acts as an ideal habitat, give it name "live rock."