Electromigration; I think that's when they use cattle prods to move herds? :lol:
Sorry My Bad, I'm in a really good mood today!
Seriously, electromigration is when the electrical pathways degrade enough to allow some electricity to short to another electrical pathway causing corruption and errors, and under some circumstances complete blowouts.
Electromigration is going to happen eventually to just about everything, it happens over time with age even to electrical motors, resulting in having to have them rewound, meaning the electrical wire inside the motor replaced, a process normally done to very expensive electrical motors, cheaper motors are just disgarded and completely replaced.
Overvolting anything will accelerate electromigration as it causes faster degradation of the electrical pathways.
There is no way to know where the breaking point is of any hardware component as some can take more voltage than others, just because of the quality of the product, and some can fail with just a small increase.
Temperature is an added factor when it comes to electromigration, lower temperatures do tend to allow more leeway than higher temperatures do, but there in again comes the quality of the component, and that's always the unknown factor.
Does over voltage cause the electrical pathways of a CPU or GPU to degrade faster, of course it does, but that's always been an acceptable loss to overclockers, willing to trade off hardware longevity for increased performance gains.
Even with that there is acceptable ground as some lean toward the conserving side, and some just flat go for it, those that completely throw caution to the wind and shoot for 24/7 max clocks, seriously increase the electromigration process, and shorten the life of the component, but for that type overclocker it was an acceptable loss.