High-density lipoprotein (HDL) is a type of cholesterol found in the blood that is often referred to as "good" cholesterol. It helps transport excess cholesterol from the arteries back to the liver, where it can be processed and removed from the body. Higher levels of HDL are associated with a lower risk of heart disease. HDL is made up of proteins and lipids, making it denser than other types of lipoproteins, such as low-density lipoprotein (LDL). Regular physical activity, a healthy diet, and avoiding tobacco can help increase HDL levels, contributing to better cardiovascular health.