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

Texinfo

   A GNU documentation system that uses a single source file to
   produce both on-line information and printed output.  You can
   read the on-line information, known as an "Info file", with
   an Info documentation-reading program.  By convention, Texinfo
   source file names end with a ".texi" or ".texinfo" extension.

   You can write and format Texinfo files into Info files within
   GNU Emacs, and read them using the Emacs Info reader.  If
   you do not have Emacs, you can format Texinfo files into Info
   files using "makeinfo" and read them using "info".  TeX is
   used to typeset Texinfo files for printing.

   Texinfo is available from your nearest GNU archive site.

   (1994-10-05)