Final answer:
The area behind the knee is called the popliteal region, which contains the popliteal vein and the popliteal fossa formed by the tendons of hamstring muscles.
Step-by-step explanation:
The area behind the knee is known as the popliteal region. This part of the leg is crucial as the popliteal vein continues from the femoral vein in this region, draining the area and forming from the fusion of the fibular and anterior and posterior tibial veins. Additionally, the popliteal fossa, which is a diamond-shaped space formed by the tendons of the hamstring muscles (biceps femoris, semitendinosus, and semimembranosus), is located in this area. These hamstring muscles are responsible for the flexion of the leg and extension of the thigh.