Definitions for overclock
To run a processor (CPU), or any electronic logic device, at a speed higher than is recommended by the manufacturer.
The New Hacker's Dictionary
To operate a CPU or other digital logic device at a rate higher than it was designed for, under the assumption that the manufacturer put some slop into the specification to account for manufacturing tolerances. Overclocking something can result in intermittent crashes, and can even burn things out, since power dissipation is directly proportional to clock frequency. People who make a hobby of this are sometimes called “overclockers”; they are thrilled that they can run their CPU a few percent faster, even though they can only tell the difference by running a benchmark program. See also case mod.