The difference between LDL (low-density lipoprotein) and HDL (high-density lipoprotein) cholesterol lies in their roles within the body. LDL is often referred to as "bad" cholesterol because it can lead to plaque buildup in arteries, increasing the risk of heart disease. In contrast, HDL is known as "good" cholesterol, as it helps transport cholesterol away from the arteries and back to the liver for excretion, thus reducing heart disease risk.