Lipids are a general term for oils, fats, and lipids. The fats and oils in food are mainly oils and fats. Generally, those that are liquid at room temperature are called oils, while those that are solid at room temperature are called fats. Fats are composed of three elements: C, H, and O. Fats are triglycerides composed of glycerol and fatty acids. The glycerol molecules are relatively simple, while the types and lengths of fatty acids are different. Fatty acids are divided into three categories: saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids. Fats are soluble in most organic solvents, but not in water.