This literally means "Oh my mother!" This is an abbreviation for 我(wo)的(de)妈(ma)呀(ya). This is typically used when someone is surprised or shocked.
Person 1: Did you hear how Shirley ate 20 fish balls?
Person 2: wdmy, how can someone eat 20 gigantic fish balls?
Person 2: wdmy, how can someone eat 20 gigantic fish balls?
by ChairmanMao69 September 19, 2021
by ChairmanMao69 October 17, 2019