What is the Printed circuit board annular ring spec?

According to the following website:

http://www.interfacebus.com/glossary-of-terms-minimum-annular-ring.htmlMinimum Annular Ring

The minimum annular ring on a plated thur-hole is the minimum amount of copper (at the narrowest point) between the hole and the edge of the pad after plating of the finished hole. MIL-STD-275E and IPC class 3 calls for a minimum annular ring of 0.05mm (0.002") edge of hole to edge of pad. MIL-STD-275E also calls out .005 inches for via to trace distance.

Minimum Annular Ring; PWB Internal Via

Both diagrams indicate minimum annular ring measured from the outside ring of the pad and to the inside diameter of the plated thru-hole for an external pad [below], or to the center of the plated via for an internal pad [above].

Minimum Annular Ring; PWB External Pad
Minimum Annular Ring applies regardless of the shape of the PCB pad. The next page shows two examples of different pad shapes.
More Printed Wiring Board Terms