What does thrombosis mean and how is it different from embolism?

Thrombosis is the formation of a blood clot, called a thrombus, inside a blood vessel that obstructs blood flow. The root thromb refers to clot and osis means abnormal condition. Deep vein thrombosis, or DVT, occurs in the deep veins of the legs. An embolism occurs when a clot or other material breaks free, travels through the bloodstream, and lodges in a distant vessel. The traveling material is called an embolus. A pulmonary embolism happens when a clot from the legs travels to the lungs and blocks a pulmonary artery.