Rotation
Movement of a bone in a single plane around its longitudinal axis. This movement is in the transverse plane.

Medial or internal rotation
is where the anterior bone surface or limb moves toward the midline of the body.

Lateral or external rotation
is where the anterior bone surface or limb moves away from the midline of the body.

See Video Demonstrations:

Neck (Multi-Bone) - Axial
Shoulder (Ball Joint) - Medial/Lateral
Wrist/Elbow (Multi Joint) - Pronation/Supination

Hip (Ball) - Lateral/Medial
Spine (Multi-bone) - Axial