The steam that is produced in the boiler has a certain percentage of moisture contnet. This moisture content is referred to as the quality of the steam. Due to the high velocities of the steam inside a turbine, the moisture content of the steam can shear the turbine blades. A superheater is utilized to remove the the moisture content in the steam. This is done by raising the temperature above while keeping the pressure constant. Steam which undergoes this process is referred to as superheated steam. The degrees of superheat is a term which is used describe the temperature difference between the raised temperature and the temperature at constant pressure. Let's clarify this further by giving an example.
Example of Degrees of Superheat:
T=350 C P=8 atm
T=612 C P=8 atm
Degrees of Superheat=612-350=272