Modulated continuous wave
Abbreviated "MCW".
"MCW uses a fixed audio tone to modulate a carrier wave."[1]
"AE’s rig did NOT have "MCW" capability (that is, A2 emission, tone modulated telegraphy). It only transmitted A1 (unmodulated, on-off keyed telegraphy) and A3 (amplitude modulated voice)" (Mike Everette, 6 September 2000, Forum).