Undervolting, or undervolt means using a lower voltage during over clocking.
All modern IC use a fixed voltage to do their work. If they need to do more work they draw more current at the same volts.
1.2v and no work = 1.2v
1.2v and working hard = 1.2v
Each of the above assumes infinite current.
The over clocking voltage dilemma starts.
A CPU is rated at a meridian voltage based around a minimum and maximum safe voltage.
As reactive loads they do not conform to R=V/I in the sense of a simple resistance. The apparent resistance is reactive to need, not voltage. CPU’s are programmed to know the voltage for a given frequency given infinite current.
More, CPU IC’s are not voltage regulators. Raise the voltage and the same frequency CPU will just dissipate, in heat, the excess. Your CPU will get hot. Try it. Up your voltage but not your clocks.
So, here we are. What is the correct voltage?
Specification of the CPU put it clearly at 4.2Ghz 1.4250v
3.9Ghz 1.3850v +_ 10% = 4.2Ghz ~1.4040v