Occlusion is a term indicating that the state of something, which is normally open, is now totally closed.

In medicine, the term is often used to refer to blood vessels, arteries or veins which have become totally blocked to any blood flow. For issues of artery occlusion, see stenosis, atheroma, and coronary catheterization.

In dentistry, the term is used to refer to the manner in which the teeth from upper and lower arches come together when the mouth is closed.