CV boot broken and leak, and causing CV join to fail. Following link show the picture and description about it Discount CV Joint - C.V. Axle, Rack and Pinion, Gearbox, or Power Steering Pump Rebuilding. CV stands for constant velocity. Each side has 1 piece. Each piece has 2 CV boots. Normally only 1 break. If you never maintain/check it, then you may not know when it brake.
Early detection of CV boot break will save you a lot of money. The boot only cost $10, while the CV join cause $200+ (depend on model).