Every gamer and even a geek wants to extract each and every drop of juice from their systems. All the systems are optimized for running at a specific speed but that speed can be increased through a way called overclocking. Wikipedia defines overclocking as follows:
Overclocking is the process of running a computer component at a higher clock rate (more clock cycles per second) than it was designed for or was specified by the manufacturer, usually practiced by personal computer enthusiasts seeking an increase in the performance of their computers.
More details about what is overclocking can be have from here.