Thrombosis is the occlusion of a vein with blood clot (thrombus). In most cases the deep veins of the legs are affected. Typical signs include pain and swelling of the calf or the whole leg, depending on the seat of thrombosis.

Deep leg and pelvic venous thrombosis

http://www.ellviva.de/Gesundheit/Venenerkrankungen-Symptome.html