Hub=the central part of a wheel
Centric=situated at or near the center; central.
Wheels not made specifically for mounting on nissan/honda/subarus etc require the use of hub centric rings. These rings fit on the inside of the wheel sandwiched between the wheel and the hub making a perfect fit.
Basically, if you get some aftermarket wheels that are made to fit multiple car types and their hubs (universal) , you will need to get hub centric rings for them to fit perfectly, otherwise they won't mount perfectly flat against the hub and can cause problems including: undue stress to wheel bearings, tire wear, vibration, etc...