Deep vein thrombosis is a type of venous thrombosis involving the formation of a blood clot in a deep vein, most commonly in the legs or pelvis. Wikipedia

Formation of a blood clot in a deep vein Wikidata

A potentially fatal condition in which one or more thrombi (or clots) form in the predominantly the leg or, more unusually, the arm. The clot may break free from the venous wall and travel via the circulatory system to the heart or to the lungs (causing a pulmonary embolism); this condition is often caused by keeping the legs bent for long periods but can also be caused by other medical problems. Wiktionary

Condition. Wiktionary (translation)