Clocking is the purpose of a clock oscillator, which is to set a rate of changes in the states or phases of logic electronics, by using a fixed or tuned type of oscillator. The rate of changes is directly related to the frequency of the clock oscillator.
over clocking is changing the clock oscillator to a higher frequency, which may require more power and generate more heat if the instrument or computer electronics were designed to run very close to the original clock speed.