He was talking about grinding the end of the rings to the proper specs that they need to be. After your cylinder is bored and honed, you put your rings down in the cylinder, making sure they are setting square in the cylinder. You measure the end gap with feeler gauges. If they're not at specs, then you have to grind the ends of the rings until the right feeler gauge fits in between them. A repair manual will list the ring end gap specs.