Grinding for surfaces of rotation (axially symmetric surfaces) can be either centered or centerless. Centered grinding involves fixturing the part on a spindle axis as it is ground, as illustrated below.
This configuration can be compared to fixturing a part on a lathe with or without a tail stock. The abrasive material is on a grinding wheel that rotates in a direction such that rolling or sliding contact occurs where the wheel and work piece touch. Centered grinding is accurate and stable, but set-up takes time and through-put suffers.