Joint fluid, also known as synovial fluid, is a thick, slippery liquid found in the cavities of joints. Its primary function is to lubricate the joints, reducing friction between the cartilage surfaces during movement. This fluid also helps to nourish the cartilage, providing essential nutrients and removing waste products. In addition to lubrication, joint fluid acts as a shock absorber, cushioning the joints during activities like walking or running. It is produced by the synovial membrane, which lines the joint capsule. Maintaining healthy levels of joint fluid is important for overall joint health and mobility.