What does the number in the various Quadrature Amplitude Modulation levels, such as 16 in...

QAM Constellations: QAM (Quadrature Amplitude Modulation) uses a constellation diagram where points represent unique combinations of amplitude and phase.

Bits per Symbol: The number in QAM-XX indicates the number of points:

QAM-16: 16 points = 2^4 = 4 bits per symbol

QAM-64: 64 points = 2^6 = 6 bits per symbol

Higher Data Rates: More points in the constellation enable transmitting more bits per symbol, leading to higher data rates at the same bandwidth.

References

QAM: https://en.wikipedia.org/wiki/Quadrature_amplitude_modulation