The term "canned tuna" refers to a type of fish that has been preserved in cans or jars. This process typically involves cleaning and cooking the fish, then placing it in an airtight container with either water or oil as a preservative. The canned tuna is then heated to create a vacuum seal before being cooled and stored for later use. Canned tuna is a popular food item that is widely available in grocery stores, and it is often used as a convenient and easy-to-prepare protein source in various dishes such as sandwiches or salads.