Maltose is a sugar that forms when starches like potatoes or rice are broken down in the digestive system. After maltose is formed, it's broken into simpler sugars so your body can use it for energy.
Most foods you eat don't have much maltose, unless you cook them. Sweet potatoes, for example, have no maltose when they're raw, but when they're cooked they have a small amount. Molasses and malted drinks like Ovaltine are some of the few uncooked food products that contain maltose. Otherwise, it forms during the digestive process. Maltose comes from malt and the chemical sugar suffix -ose.