The Free On-line Dictionary of Computing (19 January 2023):

TDF

    An intermediate language, a close relative of
   ANDF.  A TDF program is an ASCII stream describing an
   abstract syntax tree.

   TDF became part of TenDRA in abut 2001.

   ["TDF Specification", Defence Research Agency/Electronics
   Division, Great Malvern, England, +44 684 895314].

   (2003-05-13)