Sharp asked this and I know that others don't know much about it also. It used to be MUCH more common in the old days when processors were $600 for a 486. But you still can do it as long as you are willing to take the risk.
To put it in its simplest terms, overclocking is taking a computer component such as a processor and running at a specification higher than rated by the manufacturer. Every part produced by companies such as Intel and AMD are rated for a specific speeds. They have tested the capabilities of the part and certified it for that given speed. Of course, most parts are underrated for increased reliability. Overclocking a part simply takes advantage of the remaining potential out of a computer part that the manufacturer is unwilling to certify the part for but it is capable of.
The primary benefit of overclocking is additional computer performance without the increased cost. Most individuals who overclock their system either want to try and produce the fastest desktop system possible or to extend their computer power on a limited budget. In some cases, individuals are able to boost their system performance 25% or more! For example, a person may buy something like an AMD 2500+ and through careful overclocking end up with a processor that runs at the equivalent processing power as a AMD 3000+, but at a greatly reduced cost.
I ran my 2500+ at 3200+ speeds, but it sometimes became unstable. But performance gains are out there for the taking as long as you are willing to risk it.
I done it a few times to my systems over the years, but never could keep my systems cool enough to keep them stabe, so I always went back to stock timings. But I think once I get my Heat issues solved with this PC, I may see what I can get my 3500+ up to...
"Never, Never, Never quit." - Winston Churchill "Men don't like to cuddle. They only cuddle if it leads to.. You know.. Lower cuddling." - Ray Romano "Tell your wife that she looks pretty, even if she looks like a dump truck." - Ricky, age 10