He may be trying to describe the area where the comb ends at the wrist. On both sides of the stock, that area is concave. the concave continues on the cheek side right to the butt end of the cheek piece, flaring and tapering as it goes. I too use a Stanley Surform, reversed to cut on the pull, followed by a 3/8" rat-tailed cabinet maker's rasp, and then scrapers.