What sort of problem is atherosclerosis?

Disease of arteries. Atherosclerosis is an inflammatory process which occurs in arteries. Advanced stages cause narrowing of the arteries involved. The narrowing can lead to complete blockage of blood flow or to what is termed "plaque rupture" (when pieces of the lining of diseased artery break free. Clot forms and floats downstream). In the heart this causes heart attacks, in the brain this causes strokes.
Hardening of arterie. Atherosclerosis is the hardening and narrowing of the arteries, a common cause of stroke, angnia, ami etc.