What is the definition or description of: synovial fluid?

See below: Synovial fluid is a viscous, non-newtonian fluid found in the cavities of synovial joints. With its yolk-like consistency ("synovial" partially derives from ovum, latin for egg), the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement.

Joint fluid: The lining of your joints called synovium produces fluid that assists joint lubrication/nourishment. If a joint becomes injured or inflamed then excessive fluid can be produced causing joint swelling which you should check out with your sports doctor.