Rims centerbore is the size of the hole on the back of the rim. The wheel centerbore is machined to fit exactly to the hub, positioning the wheel precisely centered.
The concept of hub-centricity is important for proper selection of custom rims. A hubcentric wheel has the center bore hole of the wheel exactly matching
the vehicle's hub diameter.
If you purchase non-hubcentric wheels it is recommended that you use a hub ring and that the wheel is torqued correctly.
Properly torqued, the lug nuts will continue to keep the rims centered as the vehicle is driven.