clock rate ” Clock speeds  “ is the speed at which a microprocessor executes instructions. every computer contains an electronic clock, which produces a sequence of regular electrical pulses used by the control unit to synchronize the components of the computer and regulate the fetch-execute cycle by which program instructions are processed that regulates the rate at which instructions are executed and synchronizes all the various computer components. The CPU requires a fixed number of clock ticks (or clock cycles) to execute each instruction. The faster the clock, the more instructions the CPU can execute per second.

in other word ,  clock rate is the fundamental rate in cycles per second at which a computer performs its most basic operations such as adding two numbers or transferring a value from one processor register to another. it is the frequency of the clock in any synchronous circuit.

Clock speeds are expressed in megahertz – millions of pulses a second – (MHz)  or gigahertz (GHz).