What type of measurement using a standard multimeter measuring AC voltage will the multimeter indicate?

Multimeters measure AC in two primary ways... The older style meter uses a diode, capacitor, and resistor to measure the peak voltage of the AC signal. They then compensate their calibration to read in a close approximation of what the RMS value will be. Problem is that this only works well for true sinusoidal waveforms

• if the waveform is triangular, for instance, the indicated value

will not match the RMS value. The newer style meter, if it states that it is a true RMS meter, will sample the input waveform and actually calculate the RMS value. This is done by adding up the squares of the input, and then taking the square root of the result. That is a much better approximation of how much power the waveform can deliver.