Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Deep Vein Thrombosis ?
    ### Response:
    Deep vein thrombosis, or DVT, is a blood clot that forms in a vein deep in the body. Most deep vein clots occur in the lower leg or thigh. If the vein swells, the condition is called thrombophlebitis. A deep vein thrombosis can break loose and cause a serious problem in the lung, called a pulmonary embolism.
    