synovial fluid

Viscous colourless fluid that bathes movable joints between the bones of vertebrates. It nourishes and lubricates the cartilage at the end of each bone.

Synovial fluid is secreted by a membrane, the synovium, that links movably jointed bones. The same kind of fluid is found in bursae, the membranous sacs that buffer some joints, such as in the shoulder and hip region.