Final answer:
An embolism is a blood clot that has detached from the vessel wall and travels through the bloodstream until it lodges in a narrow vessel, obstructing blood flow and potentially causing severe medical emergencies.
Step-by-step explanation:
A blood clot that floats through the bloodstream and eventually becomes lodged in a vessel too narrow to pass, blocking blood flow, is known as an embolism. An embolus is a thrombus (blood clot) that has broken free from the blood vessel wall. This event can have serious consequences, such as a stroke, heart attack, or pulmonary embolism, which are critical medical emergencies requiring immediate attention.