Stenosis (from Ancient Greek στενός (stenós) 'narrow') is the abnormal narrowing of a blood vessel or other tubular organ or structure such as foramina and canals. It is also sometimes called a stricture (as in urethral stricture).
Stricture as a term is usually used when narrowing is caused by contraction of smooth muscle (e.g. achalasia, Prinzmetal angina); stenosis is usually used when narrowing is caused by lesion that reduces the space of lumen (e.g. atherosclerosis). The term coarctation is another synonym, but is commonly used only in the context of aortic coarctation.