Live rock is just that, rock with a variety of living creatures living in, on, around and of course off of it. The true definition of reef is a submerged ridge of rock or coral near the surface of the water. however when you wrote reef I believe you are talking about when people say "reef tank" meaning a tank with corals and invertebrates. In the saltwater end of the hobby people usually keep: FO
- Fish only, FOWLR
- Fish only with live rock, or Reef - which is usually live rock, reef safe fish and invertebrates, and corals. You will find live rock in any reef environment, naturally, and in most captive situations as well.