In medicine, an embolism occurs when an object (the embolus) or objects (emboli) migrate from one part of the body (through the circulation) and cause(s) a blockage (occlusion) of a blood vessel in another part of the body.
Blood clots form the most common embolic material by far: other possible embolic materials include fat globules, air bubbles (an air embolism), septic emboli (containing pus and bacteria), or amniotic fluid.
Assuming a normal circulation, a thrombus or other embolus formed in a systemic vein will always impact in the lungs, after passing through the right side of the heart. This forms a pulmonary embolism that can be a complication of deep-vein thrombosis.
In the rare cases where there is a congenital hole in the heart (or some other abnormality of the circulation), it is possible that an embolus from a systemic vein can cross into the arterial system and land anywhere in the body.