:TOPS-10:: /tops-ten/ n. DEC's proprietary OS for the fabled {PDP-10}
   machines, long a favorite of hackers but now effectively extinct.
   A fountain of hacker folklore; see {appendix A}.  See also {{ITS}},
   {{TOPS-20}}, {{TWENEX}}, {VMS}, {operating system}.  TOPS-10 was
   sometimes called BOTS-10 (from `bottoms-ten') as a comment on the
   inappropriateness of describing it as the top of anything.