As mentioned above, most of our body's cholesterol is actually made in the liver. Dietary fats consist mainly of triglycerides, which are made up of one glycerol molecule connected to three fatty acids. The most important structural feature of a triglyceride is the fatty acid portion. This is the segment that distinguishes one type of triglyceride, or dietary fat, from the other, both in terms of flavor and the fat's effect within the human body. Some fatty acids are saturated, some are monounsaturated, and others polyunsaturated.
Saturation simply has to do with how much hydrogen a fat contains.
Saturated fatty acids are saturated with hydrogen, or contain the maximum amount of hydrogen possible. Although they differ by just a couple of hydrogen atoms, these different types of fat behave quite differently in the body. In addition to making cholesterol, the liver is responsible for filtering LDL cholesterol from the blood. Saturated fats somehow gum up the works, either by reducing the number of LDL receptors or impairing their efficiency. On the other hand, unsaturated fats can lower blood cholesterol levels.