I guess it means someone hacked of the other 1/4 of the cam, lol. I hear that all the time in Tennessee. Apparently different cam companies would advertise there cams 3/4 or full race. I always get a laugh out of it. Typical chevy guy says, "yep, it's a 350 with four bolt mains and a 3/4 race cam and 202 double hump heads."