Joint: The area where two bones are attached for the purpose of permitting body parts to move. A joint is usually formed of fibrous connective tissue and cartilage. Joints are grouped according to their type of motion: ball-and-socket joint; hinge joint; condyloid joint, which permits all forms of angular movement except axial rotation; pivot joint; gliding joint; or saddle joint. Joints can move in only four ways: gliding, in which one bony surface glides on another, without angular or rotatory movement; angular, a movement that occurs only between long bones, increasing or decreasing the angle between the bones; circumduction, which occurs in joints composed of the head of a bone and an articular cavity, with the long bone describing a series of circles and the whole forming a cone; and rotation, in which a bone moves about a central axis without moving from this axis. Also known as articulation and arthrosis.