Final answer:
A pulmonary embolism (PE) occurs when a blood clot (thrombus) breaks off, travels through the bloodstream as an embolus, and obstructs blood flow in the lungs.
Step-by-step explanation:
The condition in which a blood clot breaks off from a large vein and travels to the blood vessels of the lung, causing an obstruction of blood flow, is known as a pulmonary embolism (PE). An embolism occurs when a portion of a thrombus, a blood clot, breaks free from the vessel wall and becomes an embolus, traveling through the bloodstream. If this embolus lodges in a pulmonary artery, it prevents deoxygenated blood from reaching the lungs for oxygenation, which can result in serious consequences, including lung damage or death.