Worldwide Harmonised Light Vehicles Test Procedure (WLTP) is the new EU emissions test procedure introduced after the Volkswagen emissions scandal in which VW implemented software to check whether the car was likely under emissions testing conditions and would reduce its output. This was caught by the United States Environmental Protection Agency prompting for other manufacturers to be tested.
WLTP tests the cars more thoroughly and under more "real world" scenarios compared to the previous testing procedure (NEDC) through the use of more test cycles, longer test durations, long test distances, high average speed test, tests under maximum speed, fixed testing temperature.
WLTP is also the reason I still haven't got my car even though I was expecting it back in October and the reason for my 306BHP Golf becoming a 296BHP Golf 😪Sad times