How does an embolism differ from thrombosis?

Both clots: Embolism is when an old clot travels from one location (heart or legs, commonly) to block a different vessel. Thrombosis is when a diseased vessel clots on its own. Embolism causes immediate problems but thrombosis can cause immediate or delayed symptoms.

One travels: An embolism travels through the blood stream lodging away from its point of origin...A thrombosis is a blood clot that stays in place.