HDL and LDL
High-density lipoproteins (HDL) are composed mainly of proteins, with only small amounts of cholesterol. HDLs are often referred to as "good cholesterol" because they help remove cholesterol from artery walls and transport it to the liver for elimination from the body. Higher HDL levels actually protect against coronary heart disease.
Low-density lipoproteins (LDL) are composed mainly of cholesterol and have very little protein. They are often referred to as "bad cholesterol" because they are primarily responsible for depositing cholesterol within arteries. High levels of LDL are associated with an increased risk for coronary heart disease.