From ICAO Doc. 8400/3 ICAO Abbreviations and Codes (which I just happen to have on my person):
QSY - "Change to transmission on another frequency (or on .....Khz/Mhz).
My favourite was always QRM - "I am being interfered with ...." followed by a number from 1 to 5 indicating the degree of interference from nil (story of my life) to extremely (dream on).
I am now QRT.