Final answer:
An obstruction caused by any foreign substance, including a blood clot within a blood vessel, is called an embolism. It can block a vessel critical to a major organ, leading to heart attacks, strokes, or pulmonary embolism.
Step-by-step explanation:
An obstruction caused by any foreign substance, including a blood clot within a blood vessel, is called an embolism. When a portion of a thrombus breaks free from the vessel wall and enters the circulation, it is referred to as an embolus. An embolism can be large enough to block a vessel critical to a major organ, causing medical emergencies such as heart attacks, strokes, or pulmonary embolism.