nicolaaa if I may be polite and say the first thing to do is identify title and then use the acronym.
Multi-level Quadrature Amplitude Modulation (“M-QAM”).
This is because in many instance people familar QoS etc in terms of 16-QAM and constellation relevant and even Quadrature Phase Shift Keying (“QPSK”).
M-QAM deal with detection of modulated signals for use in radio communication.
So help us with what it is you not understand please?