"Power oversteer" refers to a situation when a vehicle's rear wheels lose grip due to excessive power from the engine. This causes the back end of the vehicle to slide or skid out, leading to oversteering. Full definition
And the harder you punt the S4 into a bend, the better it seems to like it, especially with the Driver Select control in its Dynamic position which noticeably helps tip the nose towards the apex and even allows a degree or two of power oversteer if you're really brutal with the throttle on the exit. (evo.co.uk)
With the optional PTV Plus (an electronically controlled differential lock) fitted it will even indulge in power oversteer if you're brave enough. (evo.co.uk)
It serves as a basic form of launch control, but can also be used on the move, enabling the GT3 to be «popped» into power oversteer at low speeds. (evo.co.uk)