You use leftover to describe an amount of something that remains after the rest of it has been used or eaten. Leftover chicken makes a wonderful salad. remaining after all the rest has been used, taken, or eaten
You can refer to food that has not been eaten after a meal as leftovers. Refrigerate any leftovers
uneaten and saved for eating later; "leftover food served at a later meal"; "yesterday's reheated soup"
not used up; "leftover meatloaf"; "she had a little money left over so she went to a movie"; "some odd dollars left"; "saved the remaining sandwiches for supper"; "unexpended provisions
a small part or portion that remains after the main part no longer exists uneaten and saved for eating later; "leftover food served at a later meal"; "yesterday's reheated soup"