Differential rotation is seen if parts of a rotating object move with different angular velocity. (to put it short and non-scientific, parts at different distances from the rotation axis make a different number of rounds at a given time interval). This indicates that the object is not solid. In fluid objects, such as accretion disks this leads to shearing. Usually galaxies and protostars show also differential rotation. Also Sun, Jupiter and Saturn show differential rotation.
See also
