Clock speed
Also could be called clock rate, clock speed is the speed that the microprocessor executes each instruction or each vibration of the clock. The CPU requires a fixed number of clock ticks, or cycles, to execute each instruction. The faster the clocks rate, the faster the CPU, or the faster it can execute instructions. Clock Speeds are usually determined in MHz, 1 MHz representing 1 million cycles per second, or in GHz, 1 GHz representing 1 thousand million cycles per second.
Also see: Clock, GHz, MHz, Processor definitions