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

server-parsed HTML
sht
shtml
SPML

    (SPML, SHTML) A kind of HTML
   file containing server-specific, non-standard commands which
   are interpreted by the HTTP server and replaced by standard
   HTML or text before the data is returned to the client.

   Different servers use different command syntax and support
   different sets of commands.  The most common example is a
   server-side include command which simply expands to the
   contents of some given file and allows bits of HTML or text to
   be shared between pages for ease of updating.  Other commands
   insert the value of an environment variable or the output of
   a shell command.  These allow pages to be different each
   time they are served without requiring a CGI script.

   Some servers distinguish SPML from HTML with a different
   filename extension, others use the execute bit of the file's
   permissions.

   (1996-09-29)