The Free On-line Dictionary of Computing (19 January 2023):

MPL

   1.  An early possible name for PL/I.

   [Sammet 1969, p.542].

   2. MasPar data-parallel version of C.  See also ampl.

   Compiler version 3.1 (ftp://maspar.maspar.com/put/).

   3. Motorola Programming Language.  A low-level PL/I-like
   language, similar to PL/M, but for the Motorola 6800.

   4. MicroProgramming Language.  Simple language for
   microprogramming.  Statements on the same line represent
   register transfers caused by one microinstruction, and are
   executed in parallel.

   ["Structured Computer Organization", A.S. Tanenbaum, First
   Edition, P-H 1976. (Replaced in later editions by Mic-1)].

   (1995-03-07)