What does overclocking do?
http://en.wikipedia.org/wiki/OverclockingOverclocking is the process of making a computer or component operate faster than the clock frequency specified by the manufacturer by modifying system parameters. One of the most important techniques is running at a higher clock rate (more clock cycles per second; hence the name "overclocking"), but other parameters, such as CPU multiplier and memory timings, can also be changed and would be considered to be overclocking. Operating voltages may also be changed (increased), which can increase the speed at which operation remains stable. Most overclocking techniques increase power consumption, generating more heat, which must be dispersed if the chip is to remain operational.
TL;DR makes your chip (CPU, GPU, APU etc) go faster than it's stock speed, which creates more heat (and in some cases, less stability) but also gives you a huge performance increase.
My Intel i5-2500K (the K series are factory unlocked, and designed for overclocking) comes stock at 3.4 GHz, I've overclocked it to 4.5GHz. To compensate for heat, I've added a Corsair Hydro series H100 water cooling kit to keep the processor in safe temperatures.
Poll