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

P-code

    The intermediate language produced by the
   Pascal-P compiler.  P-code is the assembly language for
   a hypothetical stack machine, the P-machine, said to imitate
   the instruction set of the Burroughs 6700.

   The term was first used in the Wirth reference below.  Byte
   articles on writing a Pascal Compiler in Northstar BASIC (ca
   Aug 1978) also used the term.

   P-code was initially the intermediate code generated by the P2
   compiler from ETH Zurich.  P-code was later used as the
   intermediate language in the UCSD Pascal System, and in its
   two main derivatives, Apple Pascal and the UCSD P-system.

   Variants: P2 P-code, P4 P-code, UCSD P-code, LASL P-code.

   [Algorithms + Data Structures = Programs, N. Wirth, P-H 1976].

   ["A Comparison of PASCAL Intermediate Languages", P.A. Nelson,
   SIGPLAN Notices 14(8):208-213, Aug 1979].

   (2004-11-08)