The Free On-line Dictionary of Computing (30 December 2018):

Tcode

   Intermediate language used by the Spineless Tagless G-machine
   (an abstract machine based on graph reduction) designed as a
   target for compilation of non-strict functional languages.
   "The Spineless tagless G- machine", S. Peyton Jones et al,
   Fourth Intl Conf Func Prog Langs and Comp Arch pp.184-201, ACM
   Sept 1989.