The iliotibial band (ITB) is on the outer aspect of the knee. This video shows how to do an ITB stretch.




In case you cannot see the video, here is a still sequence -

ITB stretch The left leg is the one being stretched. Stand comfortably next to a wall, and support yourself with one hand on the wall.
ITB stretch Keep your weight on the right leg while you stretch your left leg behind it.
ITB stretch Bend the right leg (in front) to apply stretch to the left leg (at the back). Hold the stretch for a few seconds.
ITB stretch Bring the legs back to the starting position.
ITB stretch To stretch the other leg you will need to turn round and face the other way.