All the various AC voltage values (RMS, peak. average, effective, etc) can be quite confusing to newcomers to electronics. The math can be a bit confusing also and terms like creast factor let alone distortion products can make what should be a simple measurement somewhat mystical.
I had someone explain to me many decades ago that the true RMS value of any AC wave form is such that it would dissapate the identical amount of heat energy as the same value of DC voltage if connected to the same value resistive load. That helped me get at least a start on understanding the theory and measurement practices of AC voltages.
Of course when the load changes to reactive elements then a whole new set confusing factors began for me