Final answer:
An embolus is a piece of a thrombus that has broken free from a blood vessel wall and is circulating in the bloodstream. It can block a vessel and cause an embolism, such as deep vein thrombosis or a pulmonary embolism.
Step-by-step explanation:
If part of a blood clot is dislodged and circulates through the bloodstream, it is called an embolus. When a thrombus, which is an aggregation of platelets, erythrocytes, and white blood cells (WBCs) trapped within a mass of fibrin, breaks free from the blood vessel wall and begins to move through the circulatory system, it becomes an embolus. An embolus can travel through the bloodstream and may eventually block a vessel critical to a major organ such as the heart, brain, or lungs. When it lodges in a vessel and blocks blood flow, an embolus is referred to as an embolism. Conditions such as deep vein thrombosis (DVT) and pulmonary embolism (PE) are the result of such blockages and are considered medical emergencies.