Object Properties
The value for the outer radius defines the overall size of the disc. A value for the inner radius of greater than zero generates a perforated disc. The inner radius can be no larger than the outer radius.
Disc Segments gives the radial subdivision, Rotation Segments the subdivision along the circumference.
Discs with different subdivisions.
These options define the direction in which the object will "point". Using these options it is easier - and faster - to rotate the object (without rotating the object coordinate system as well).