WARM UP LEFTOVERS refers to the process of reheating food that has been cooked and stored in the refrigerator. Reheating leftovers is a great way to save time and money, as well as reduce food waste. The term WARM UP LEFTOVERS is often used to describe the process of reheating food that has been cooked and stored in the refrigerator. This process can be done in a variety of ways, such as in the oven, on the stovetop, or in the microwave.