The "RMS" means the Root Mean Square. It is calculated using the fundamental and harmonic components of the voltages or currents. All the fundamental and harmonic components are effective values corresponding to the steady-state operating condition, which are not the transient values (for example, transient values could be the peak value of the sine wave voltage waveform).
In the cases that the harmonic ...
This solution explains how RMS is calculated. The solution explains the types of connections that three-phase electrical systems can have and the reason all three-phase equipment ratings refer to the line-to-line voltages. 250 words.