1. A process of progressive thickening and hardening of the walls of medium-sized and large arteries as a result of fat deposits on their inner lining.
2. The accumulation of fatty material, cholesterol, and other substances on the interior walls of the arteries.

This build-up, known as plaque, reduces the elasticity of the vessel wall ("hardening of the arteries"), and impedes blood flow through the vessel.

Atherosclerosis can also trigger the formation of blood clots, which can detach and cause blockage in arteries of the heart, brain, or lungs, leading to heart attack or stroke. Similarly, plaque material can break off and travel through the blood system to obstruct a vessel elsewhere.

It is a progressive disease beginning in childhood, but symptoms, including angina and leg pain, do not begin usually until later in life. Risk factors include high levels of blood cholesterol (especially, low-density lipoproteins, or "bad" cholesterol), diabetes, high blood pressure, smoking, obesity, and lack of exercise.

3. A form of arteriosclerosis characterized by the deposition of atheromatous plaques containing cholesterol and lipids on the innermost layer of the walls of large and medium-sized arteries.

Atherosclerosis is responsible for much coronary artery disease (angina and heart attacks) and many strokes.