What does Sgl Ref-A-M Clr 6mm window stand for?

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These windows on the BCL come directly from the E+ dataset WindowConstruct.idf. The nomenclature used is described atop the file, for Ref-X,Y see WindowConstructs.idf#L18:

! Ref-X-Y        One pane has a metallic reflective coating where:
!                  X=A: stainless steel coating
!                    B: titanium coating
!                    C: pewter coating
!                    D: tin-oxide coating
!                  Y=L: low-transmittance coating
!                    M: medium-transmittance coating
!                    H: high-transmittance coating

This file also has a comment atop each window construction that gives a few parameters, here's for your first one, WindowConstructs.idf#L128

  ! U=4.664  SHGC=0.261  TSOL=0.11  TVIS=0.14

  Construction,
    Sgl Ref-A-M Clr 6mm,     !- Name
    REF A CLEAR MID 6MM; !- Outside Layer

All but one of these parameters are also on the BCL, here is the same window, you'll see it has the U, SGHC and TVIS information as metadata too.

Edit: Interestingly enough, the "Description" field should have given you the answer, I quote:

Description: Window construction from EnergyPlus 8.0 WindowConstructs.idf dataset.