Joints (Articulations): The unions between two or more bones or cartilages.

Abduction: Type of motion that occurs when a limb or limb segment moves away from the body midline.

Adduction: Type of motion that occurs when a limb or limb segment moves toward the body midline.

Bone congruence: The degree to which bone surfaces at joints are in contact.

Cartilage: A flexible connective tissue found in many areas in the human body.

Extension: Occurs when the angle between the bones meeting at a joint increases (becomes more obtuse).

Flexion: Occurs when the angle between the bones meeting at a joint decreases (becomes more acute).

Fibrous connective tissue: Unites bones meeting at fibrous joints and fills the spaces between them. This type of tissue, for instance, unites the bones of the skull and attaches the teeth to the jaw.

External rotation: Occurs when a limb or limb segment turns around its longitudinal axis away from the midline. 

Internal rotation: Occurs when a limb or limb segment turns around its longitudinal axis toward the midline.

Synovial joints: These are joints characterized by the existence of capsules surrounding articulating surfaces and lubricating fluid within those capsules. Their motion is determined by the shapes of the bone articular ends meeting at the joint and the ligaments and other structures limiting motion. Includes ball and socket joints, condyloid joints, hinge joints, pivot joints, plane joints, and saddle joints.

Ball and socket joint: A type of synovial joint, it is the only type of joint that permits motion in three axes.

Condyloid joint: A type of synovial joint.

Hinge joint: A type of synovial joint, the hinge joint permits motion in one axis (flexion and extension). Examples include the knee and elbow.

Pivot joint: A type of synovial joint.

Plane joint: A type of synovial joint, plane joints permit the gliding of structures.

 and 

Saddle joint: A type of synovial joint.