What´s the PG rail on PSU?

There is one grey wire on PSU´s - the PG rail or PWR_OK
Any1 can explain me the function of this wire?
Thanks.

The PG rail is asserted to 5v when the PSU is operating within normal parameters. It is typically asserted 100-500ms after Power_On has been held low and the PSU has turned on.

In the case of overload or overheat or overvoltage, the PSU will de-assert PG and the voltage will drop to 0v on that line, or the PSU switches off.

The Motherboard responds to PG like so - When PG is asserted at turn-on, the Motherboard starts the POST and bootup routine. If PG is de-asserted when the computer is on then the motherboard will reset the system, or turn itself off.

Thanks,
so the PSU controls the PG...
in case of overload PSU decrease PG to 0V and mobo responds to this by doing a shut down (if on Win) or just turn power off?