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.