File this one under the "I'm sorry I asked" category. In other words, it's the place on the outside of the knee where the tendons meet that help the knee flex back and forth.
I actually had to look online for images to get a good idea of what this really was. I didn't think the article described it in layman's terms perhaps as well as it could have. Makes me wonder if a medical student wrote it.
It's one of those things that had to have a name, I suppose, so it got the name of the doctor who really paid attention to it first. That's medicine for you.