Apple Betty is a style of baked fruit dessert, having alternating layers of buttered bread crumbs and spiced, sweetened fruit. Apples are by far and away the most common fruit used. You will often see it called “Apple Brown Betty” (“brown” coming from the brown sugar used.)
Some people make their topping out of flour and butter instead of breadcrumbs and call it a Betty, but what they actually have made is a crumble. Not that I mind; if it’s on the table and I didn’t have to cook it, they can call it anything they want.
Betty was very popular in Colonial America, as it could be made in the rudimentary ovens and pots the colonialists still had.