Sauce apples are those apples deemed by cooks and home canners to be varieties which perform well when used to make applesauce.
You can boil almost any apple down into a sauce, if you cook it long enough. However, the best sauce apples are those that have a soft enough flesh to break down with only little cooking, meaning that less taste is lost.
A Charles Ross Apple is a good example of an apple that won’t lose its shape easily to break down into sauce; this makes the Charles Ross apple a better cooking apple for pies, where you want the shape maintained.
Apples that are good for making sauce with are also good for making apple butter with.