Fats are a type of nutrient and lipid commonly found in living beings and food, usually composed of molecules called triglycerides—three fatty acid molecules joined to a glycerol molecule. Fats can be solid or semi-solid at room temperature and provide a dense source of energy, offering about nine calories per gram, which is more than double the calories in carbohydrates or proteins. They serve several vital functions including energy storage, building cell membranes, insulating body organs, maintaining body temperature, and supporting hormone production. There are different types of fats: saturated fats (mostly from animal products and some plants), unsaturated fats (found in plant oils and fish, including monounsaturated and polyunsaturated fats), and trans fats (mostly industrially created, which can be harmful). Essential fatty acids, such as omega-3 and omega-6, are types of fats the human body cannot produce and must obtain from diet. Fats also assist in absorbing fat-soluble vitamins A, D, E, and K, making them indispensable for overall health and development. In summary, fats are essential biological compounds used for energy, structural functions, and various metabolic roles, and they vary in their health effects depending on their chemical structure and source.