Kellogg's introduced Pop-Tarts in 1964 as a shelf-stable toaster pastry.
The product was developed after Post introduced Country Squares, a similar pastry that was not yet ready for production. Kellogg's refined the idea and launched Pop-Tarts in four flavors: apple-currant, blueberry, brown sugar cinnamon, and strawberry.
Pop-Tarts were designed to be heated in a toaster, although they can also be eaten directly from the package. Their frosting was added later because early versions were not intended for toaster heating.
The name combines “pop,” referring to the pastry popping up from a toaster, with “tarts.” The product became one of Kellogg's best-known breakfast brands, but it is technically a filled pastry rather than a conventional breakfast cereal.