What is the definition or description of: d dimer?

Marker for clot: D-diner is a breakdown product from blood clots. It can be found elevated in certain conditions like pulmonary embolus (blood clot which travels to the lung) deep venous thrombosis (blood clot in deep vein of legs usually) and disseminated intravascular coagulation (diffuse clot formation from severe infection which actually leads to bleeding).