Quick Answer: Seafood is any form of sea life regarded as food by humans, prominently including fish and shellfish. Shellfish include various species of molluscs, crustaceans, and echinoderms. Historically, marine mammals such as cetaceans as well as seals have been eaten as food, though that happens to a lesser extent in modern times. Edible sea plants such as some seaweeds and microalgae are widely eaten as sea vegetables around the world, especially in Asia. Seafood is an important source of protein in many diets around the world, especially in coastal areas. Semi-vegetarians who consume seafood as the only source of meat are said to adhere to pescetarianism. The harvesting of wild seafood is usually known as fishing or hunting, while the cultivation and farming of seafood is known as aquaculture and fish farming. Most of the seafood harvest is consumed by humans, but a significant proportion is used as fish food to farm other fish or rear farm animals.