Atherosclerosis is a condition where plaque builds up in the arteries, narrowing them and reducing blood flow. It develops as cholesterol builds up under the damaged artery lining, causing inflammation and formation of fatty deposits called plaque. Major risk factors include high blood pressure, high cholesterol, smoking, and high blood sugar. Treatment focuses on lifestyle changes like a healthy diet, exercise, and quitting smoking as well as medications and sometimes surgery to open blocked arteries and reduce complications.