We must limit ourselves to eight character names, for compatibility with DOS filesystems and the ISO 9660 standard used for CD-ROM distribution. TT represents the typeface name. W represents the weight.
Many fonts have more than one variant.
N represents the encoding, and is omitted if the encoding is nonstandard. The weight, variants, and width are probably all best taken from the original name of the font, instead of trying to relate them to some external standard.