Going

The individual Going or Run of a step is measured from face of riser to face of riser or from edge of nosing to edge of nosing in plan view. A person using the stairs would move this distance forward with each step they take. The total Run or total Going of the stairs is the horizontal distance from the first riser to the last riser. It is not simply the sum of the individual tread lengths due to nosing overlapping between treads.

WIKIPEDIA ENTRY FOR STAIRWAY

Stair Rise 2 Picture