MCTs are a type of fat. Just as there are types of sugar made up of a combination of sugars (glucose and fructose = sucrose) and types of proteins made up of various amino acids, there are also different types of fats that are defined by their composition of fatty acids and by their size.
What sets MCT (medium-chain triglycerides) apart is its size. MCTs contain between six and 12 carbons, while long-chained fats, such as the omega-3 fats docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), have 13 to 21 carbons.
Your body processes MCT quicker and more efficiently than long-chain fats in your diet.
Normally, a fat taken into your body must be mixed with the bile released from your gallbladder and acted on by pancreatic enzymes to break it down in your digestive system. These long-chain fats are transported to the lymphatic system where they circulate and end up in your liver or are easily stored in adipose tissue throughout the body.
Because MCTs can bypass "normal" fat digestion and go directly to the liver, MCTs are readily used by your body for energy, rather than being stored as fat.