Reference:Disc

Another flat, finite object available with POV-Ray is the disc. The disc is infinitely thin, it has no thickness. If you want a disc with true thickness you should use a very short cylinder. A disc shape may be defined by:

DISC:
  disc {
    <Center>, <Normal>, Radius [, Hole_Radius]
    [OBJECT_MODIFIERS...]
    }

Disc default values:

HOLE RADIUS : 0.0

The vector <Center> defines the x, y, z coordinates of the center of the disc. The <Normal> vector describes its orientation by describing its surface normal vector. This is followed by a float specifying the Radius. This may be optionally followed by another float specifying the radius of a hole to be cut from the center of the disc.

Note: The inside of a disc is the inside of the plane that contains the disc. Also note that it is not constrained by the radius of the disc.