Confusion about the rated voltage of a Permanent magnet synchronous motor
It depends on whether the motor is designed to be operated from an AC or DC source. If the motor is rated for 24V DC then rms doesn't apply, because rms and peak voltage are the same for DC. If it is supposed to work off AC power (either directly or through an inverter) then that AC power would normally be measured in rms. 

A PMSM designed for DC operation a usually called a brushless DC motor (BLDC) while one designed for AC operation is normally described as a brushless AC motor. But these terms are not exclusive. BLDC could refer to any motor that doesn't have brushes and runs from a DC source (either directly or through a controller) - including variable reluctance, stepper, and voice coil motors - while brushless AC includes induction and hysteresis motors that don't have permanent magnets.        

Most low voltage 'BLDC' motors are intended to be driven with '6 step' commutation, which produces a trapezoid drive waveform. These motors often have non-sinusoidal back-emf because they are designed to work best with trapezoid drive. Low voltage brushless motors described as 'PMSM' are usually intended to be driven with sine waves. 

However both types of motor can be driven with either waveform, the only difference being that on trapezoid drive a PMSM will produce higher than rated speed with greater torque ripple, while on sine wave drive a 'trapezoid' BLDC motor will have lower than expected performance. So it is possible to describe the same motor as both BLDC and PMSM, and even rate it differently depending whether it is driven with 'AC' (sine waves)  or 'DC' (6 step commutation).