Final answer:
An embolus is a portion of a blood clot that breaks free and enters the bloodstream. It can block a vessel, causing an embolism and leading to serious medical conditions such as a heart attack, stroke, or pulmonary embolism.
Step-by-step explanation:
An embolus is a portion of a thrombus (blood clot) that breaks free from the vessel wall and enters the circulation. It can be large enough to block a critical vessel, causing an embolism. In the heart, brain, or lungs, an embolism can lead to a heart attack, stroke, or pulmonary embolism, which are medical emergencies.