What is the difference between a regular saltwater tank and a reef tank?

A regular saltwater tank is often referred to as a fish only or fish only with live rock tank. The abbreviations for these types of tanks are "FO" for fish only or "FOWLR" for fish only with live rock. Reef tanks are similar to fish only tanks but have additional life in the form of corals. Corals can be quite demanding to keep and often require specialized lighting and filtration. The addition of corals to a marine aquarium can produce a stunningly beautiful seacape.