What's a labrum?

The shoulder joint has a cuff of cartilage called a labrum that forms a cup for the end of the arm bone (humerus) to move within. Well I just found out that I have torn mine. I do not know alot about it at this point, except it does explain the severe pain I have had in my left shoulder and arm for two weeks. I see an orthopedic surgeon on Monday and will let everyone know more then. Guess I've done a little too much yardwork?