Live Rock is used to provide a background in marine aquariums.
Live Rock refers to the skeletons of long dead corals. These skeletons are composed of calcium carbonate. Contrary to what many people imagine, Live Rock is not actually "live". What makes it live are the many microscopic algae, bacteria and tiny invertebrates that live in it.
The bacteria serve as biological filters and breakdown the ammonia and the nitrites. Live Rock help in making the aquarium resemble a natural sea environment.
Live Rock is obtained from coral reefs from the seas. There are different types of Live Rock depending on the place they come from such as Fiji Live Rock, Tonga Live Rock and so on.
Live Rock should be obtained ethically. In many parts of the world, unscrupulous dealers break live coral and sell it to hobbyists. This is illegal in many places.
Most Genuine products are collected passively which means that the rocks break off naturally due to tidal and wave action and wash ashore.