The Jargon File (version 4.4.7, 29 Dec 2003):

PDP-10
 n.

    [Programmed Data Processor model 10] The machine that made timesharing
    real. It looms large in hacker folklore because of its adoption in the
    mid-1970s by many university computing facilities and research labs,
    including the MIT AI Lab, Stanford, and CMU. Some aspects of the
    instruction set (most notably the bit-field instructions) are still
    considered unsurpassed. The 10 was eventually eclipsed by the VAX
    machines (descendants of the PDP-11) when DEC recognized that the 10
    and VAX product lines were competing with each other and decided to
    concentrate its software development effort on the more profitable VAX.
    The machine was finally dropped from DEC's line in 1983, following the
    failure of the Jupiter Project at DEC to build a viable new model. (Some
    attempts by other companies to market clones came to nothing; see Foonly
    and Mars.) This event spelled the doom of ITS and the technical
    cultures that had spawned the original Jargon File, but by mid-1991 it had
    become something of a badge of honorable old-timerhood among hackers to
    have cut one's teeth on a PDP-10. See TOPS-10, ITS, BLT, DDT, EXCH
    , HAKMEM, pop, push. See also http://www.inwap.com/pdp10/.


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

PDP-10

    Programmed Data Processor model 10.

   The series of mainframes from DEC that made time-sharing
   real.  It looms large in hacker folklore because of its
   adoption in the mid-1970s by many university computing
   facilities and research labs, including the MIT AI Lab,
   Stanford, and CMU.  Some aspects of the instruction set
   (most notably the bit-field instructions) are still considered
   unsurpassed.

   The PDP-10 was eventually eclipsed by the VAX machines
   (descendants of the PDP-11) when DEC recognised that the
   PDP-10 and VAX product lines were competing with each other
   and decided to concentrate its software development effort on
   the more profitable VAX.  The machine was finally dropped from
   DEC's line in 1983, following the failure of the Jupiter
   Project at DEC to build a viable new model.  (Some attempts by
   other companies to market clones came to nothing; see Foonly
   and Mars.)  This event spelled the doom of ITS and the
   technical cultures that had spawned the original Jargon
   File, but by mid-1991 it had become something of a badge of
   honourable old-timerhood among hackers to have cut one's teeth
   on a PDP-10.

   See TOPS-10, AOS, BLT, DDT, DPB, EXCH, HAKMEM,
   JFCL, LDB, pop, push.

   news:alt.sys.pdp10

   [Was the PDP-10 a mini or a mainframe?]

   (2001-01-05)