Atherosclerosis. Diagram is courtesy of U.S. Department of Health & Human Services National Institutes of Health.
Atherosclerosis is a clogging, narrowing and hardening of the body's large and medium-sized blood vessels. Atherosclerosis can lead to hypertension, stroke, myocardial infarction, renal problems, etc. Not surprisingly, cardiovascular risk markers tend to reflect a person's degree of atherosclerosis.
Atherosclerosis is actually a chronic inflammatory response within the walls of arteries. Small lipoproteins like LDL are able to diffuse through the endothelial wall of blood vessels and accumulate. The inflammatory component of atherosclerosis results from the migration of leukocytes (mainly macrophages) that enter the blood vessel walls. These macrophages seek to remove the deposited LDL as well as intermediate-density lipoproteins (IDL). As macrophages phagocytose these lipoproteins, they become foam cells that get trapped in the endothelial space. This eventually leads to "hardening" or "furring" of the arteries and plaque formation.
Arteriosclerosis is a general term describing any hardening (loss of elasticity) of medium or large arteries whereas atherosclerosis is a hardening of an artery specifically due to plaque. The risk to patients with significant atherosclerosis is that eventually a narrowing of the artery (stenosis) can cause a reduction in oxygen delivery to tissues and plaque rupture can lead to an acute coronary event.