Per bowl.com:
"the radius of gyration determines how easy it is for the bowling ball of particular weight to rotate about a given axis and is a measurement of where the weight is located inside the ball relative to the center.
To help explain this concept further, imagine a figure skater twirling on the ice. If the skater spins with arms extended out, the rate of rotation is slower than if the arms are pulled inward toward the body. The same physics principle applies for a designed core inside of a bowling ball. For a given core shape, the more dense (heavier) the inner core becomes, the more the bowling ball will simulate rotation like a figure skater with arms tucked close the body. In other words, the core will have a low RG and will help the ball rev up quickly. The less dense (lighter) the inner core, the more the ball will behave as a spinning figure skater with arms extended out and it will take longer for the ball to rev up as it travels down the lane, thus, having a higher RG. The low RG ball allows friction with the lane to add to rotation for a sooner and more arcing break point. The high RG ball will resist rotation longer than the low RG and it becomes harder for friction to add to the ball's rotation, resulting in a ball that slides further down lane before hooking. The radius of gyration is measured in inches. The USBC has a lower limit of 2.43 inches and an upper limit of 2.80 inches. More aggressive bowling balls on the market have an RG close to the lower limit, while plastic balls will have an RG value near the upper limit."
Summary: A lower RG number means the ball will want to rev up sooner and be a little less angular at the breakpoint. A higher RG number means the ball will push down the lane longer before revving up and will have a little more angular breakpoint.
