An oyster is a type of shellfish that lives in the ocean, encased in a rough, irregularly shaped shell made of two hinged halves. Inside that hard exterior lies soft flesh that people have eaten for thousands of years. Oysters attach themselves to rocks, other oysters, or specially built structures, filtering tiny particles of food from the seawater that flows past them.

These creatures play an important role in keeping ocean water clean: a single oyster can filter up to 50 gallons of water per day. Oyster reefs also provide homes and protection for many other marine animals, making them crucial to healthy coastal ecosystems.

People eat oysters raw, steamed, fried, or baked. Some oysters produce pearls, beautiful round gems that form when a grain of sand or other irritant gets trapped inside the shell and the oyster coats it with smooth layers over time. Natural pearls are rare and valuable, which is why people sometimes say the world is your oyster when you have many opportunities ahead of you, like an oyster that might contain a precious pearl.

Oyster farming, called aquaculture, is a major industry in coastal areas. Farmers grow oysters on ropes or in cages underwater, harvesting them when they reach the right size for eating.