Final answer:
An aneurysm is a sac formed by the dilation of a blood vessel, usually an artery, that is filled with blood. This is distinct from a thrombus, which is a stationary blood clot that can lead to an embolism if it becomes dislodged and obstructs blood flow in vital organs.
Step-by-step explanation:
A sac formed by dilation of a blood vessel, usually an artery, and filled with blood is known as an aneurysm. Unlike a thrombus, which is a clot that remains attached to a blood vessel wall, an aneurysm is a bulging section in the wall of an artery that has become weakened and is at risk of rupturing. A thrombus is an aggregation of clots that can impede blood flow and potentially lead to medical emergencies, such as a stroke, if it becomes dislodged and forms an embolus, which is a thrombus that travels through the bloodstream and can cause blockages in critical vessels of major organs like the heart or lungs.