What is "filet-o-fish"

The Filet-O-Fish is a fish burger sold by the international fast food chain store McDonald's. It was invented in 1962 by Lou Groen, a McDonald's franchise owner in Cincinnati, Ohio. While the fish composition of the sandwich has changed through the years to satisfy taste and supply shortcomings, the framework of its ingredients have remained the same; a fried breaded fish fillet, steamed bun, tartar sauce, and pasteurized processed American cheese.