Osteoarthritis is the same thing as degenerative arthritis. It's the most common form of arthritis. It happens in most of us as we grow older, but can also be found in younger people. It can be caused by trauma to the joint, repetitive use (runners are prone to oa of the knee, for instance) or simply the wear and tear of time.
OA is generally treated with analgesics, heat or cold and judicious use of exercise. Non-weight bearing exercise is preferred; swimming is a terrific way to keep the joints functioning as well as possible.
Here is a link to the Mayo page on OA for more information.http://www.mayoclinic.com/health/osteoarthritis/DS00019