High-density lipoprotein

The high-density lipoproteins are complex groups of protein molecules responsible for transporting fat molecules through the body when they are in a water environment. They exclusively transport fat that is being removed from other cells. They are typically made up of anywhere from 80 to 100 protein molecules. They are divided into five groups based on their density and size. 
In medical science, high HDL levels have been found to be beneficial as they prevent the buildup of arterial plaque and are a good indicator the patient is not at risk for atherosclerosis. 
High-density lipoprotein at Wikipedia