Multiple order waveplate means the retardance of a light path will undergo a certain number of full wavelength shifts in addition to the fractional design retardance.
The thickness of multi order waveplate is always around 0.5mm. Compared with zero order waveplate, multi order waveplate is more sensitive to wavelength and temperature changes. However, they are less expensive and widely used in many applications where the increased sensitivities are not critical.