You can overclock a CPU, but the speed it is sold at (stock speed) is what it has been designed for.
Past that speed, there is no guarantee that it will not be damaged.
Overclocking can get you a good increase in speed for free, but you must be extremely careful.
If you go too far or too fast, you risk frying the CPU and/or other components.
It depends on the CPU and cooling, as well as the room temperature, as to how far you can overclock.
Does that go some way towards answering your question?