What do these units mean? I don’t know what this simulation result means?

What does RMS{D(x,y,z,f(0))} and Re{Ez,exp(jβ)} mean?

Re{Ez,exp(jβ)} is the real part of the z-component of the electric field
and RMS{D(x,y,z,f(0))} is the root mean square of the displacement field which is defined as D = permittivity*E.
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