Synovial fluid is also called synovium. It is a viscous liquid located in the joints that forms a film on the inner surfaces of the joint capsule. The synovial fluid has several functions: to limit the friction between bones (lubricant function), to absorb shocks, to supply nutrients and oxygen necessary for the chondrocytes, to eliminate metabolic waste and possible foreign bodies thanks to the phagocytes that it contains. 

Synovia is secreted by the cells of the synovial membrane called synoviocytes. It is composed of serum dialysate. The composition and texture of the synovial fluid varies according to the patient's state of health. Thus, during inflammation, the synovial fluid has a more or less white, cloudy appearance and loses its viscous properties.  Synovial effusion is the accumulation of synovial fluid which is characterised by a swelling of the joint. It is usually located in the knee.