At the moment, most implementations of TeX look up a TFM file (as
part of the \font command), by searching for a file with the name
given by the user (possibly in any of series of directories). But if we
also looked TFM names up in another file (or set of files), which
specifies the actual filename, the fontname given in the TeX source
file could be almost anything at all, of any length.
In version 5.851d of Web2c, I implemented this mapping file. Each file
texfonts.map in a search path is read for abbreviations. The file
has a straightforward format: each line specifies the filename and the
TeX name for one font, separated by whitespace. Extra information on
the line is ignored; then more information could be specified for the
benefit of DVI-reading programs in the same file. Comments start with
% and continue to the end of the line.
Besides allowing long names, this sort of mapping file has other benefits. TeX source or DVI files can be more easily transported, because the font names in a particular file can be made to work on every system. Also, when combined with a consistent naming scheme, macros could be written to access any of a number of fonts. Right now, each font family has to have specialized macros written to deal with it.
Incidentally, Professor Knuth has approved this as a legitimate “system-dependent” extension; a TeX with such a feature can still be called “TeX”.