A professional wrestling term referring to the part of the leg that gets damaged by a number of different wrestling moves - that is, nothing at all.
Unlike the medial collateral ligament, which is exists and is an important and fun part of the upper leg, the medial collateral LATERAL ligament is totally BS. The careful listener and reader will note that the word "medial" refers to being in the middle or center, and the word "lateral" means on the side.
But it does roll of the tongue, especially the tongue of Gorilla Monsoon. See Gorilla Monsoon vs. Bobby Heenan for some examples.