The iliotibial band is a fascia that runs from the outside of the pelvis to the lower knee and inserts into the top of the tibia. It functions as a hip abductor and stabilizes the knee while running. Unlike a muscle, the IT band is not particularly malleable, and it is highly innervated.
When the IT band becomes tight or inflamed, it creates friction as it rubs against the outer portion of the upper tibia, which causes pain on the outside of the knee. This injury occurs commonly in runners, and responds well to several conservative treatments, including Active Release Techniques, Graston, and massage therapy.
The link below lists several treatment options, including rolling, massage, and changes you can make to your stride to reduce the risk of inflammation.