extrude hone is actually a brand name more that anything else but it also describes the process pretty well
basically it "hones" the piece by "extruding" abrasive material through the piece, as far as i know it can only be done to the inside of parts like intake and exhaust manifolds. it removes casting flash and more. the more passes they make with it the more material is removed. from what i have heard the "abrasive material" that they use is kind of like silly putty with some sort of abrasive like aluminum oxide or something mixed into it.