Processed food refers to any food that has undergone changes from its natural state. This can include various methods such as cooking, freezing, canning, or adding preservatives, flavorings, or other ingredients. These alterations are done to enhance the taste, texture, shelf life, or convenience of the food. Therefore, the correct answer is "A food not in its natural state" and "A food that has been changed", as they accurately describe the concept of processed food.