A spotface often takes the form of a very shallow counterbore.

This is in contrast to the ASME Y14.5-2009 definition of a spotface, which is equal to the flat seat diameter.

A spotface or spot face is a machined feature in which a certain region of the workpiece (a spot) is faced, providing a smooth, flat, accurately located surface.

But in CNC machining this is irrelevant, because the flat spotface is left by circular interpolation of the endmill as it traces a circular toolpath in the XY plane.

This is especially relevant on workpieces cast or forged, where the spotface's smooth, flat, accurately located surface stands in distinction to the surrounding surface whose roughness, flatness, and location are subject to wider tolerances and thus not assured with a machining level of precision.