vcore is one of the two electrical factors in a split voltage microcircuit, usually a CPU; the other factor being vio. vcore stand for Voltage Core, and is the voltage applied to the chip to power the internal circuitry inside the chip alone. Most motherboards run at 3.3 volts, but modern CPU's would burn themselves up when you couple that high of a voltage with the clock speeds that todays microprocessors reach. So, the CPU<->Bus signalling will be (usually) run at 3.3 volts (this is where vio comes in) while the CPU's internals will be run at a much lower voltage to reduce heat and increase clock speed.