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

abstract machine

   1.  A processor design which is not intended to be
   implemented as hardware, but which is the notional executor
   of a particular intermediate language (abstract machine
   language) used in a compiler or interpreter.  An abstract
   machine has an instruction set, a register set and a model
   of memory.  It may provide instructions which are closer to
   the language being compiled than any physical computer or it
   may be used to make the language implementation easier to
   port to other platforms.

   A virtual machine is an abstract machine for which an
   interpreter exists.

   Examples: ABC, Abstract Machine Notation, ALF, CAML,
   F-code, FP/M, Hermes, LOWL,
   Christmas, SDL, S-K reduction machine, SECD, Tbl,
   Tcode, TL0, WAM.

   2.  A procedure for executing a set of instructions in
   some formal language, possibly also taking in input data and
   producing output.  Such abstract machines are not intended to
   be constructed as hardware but are used in thought
   experiments about computability.

   Examples: Finite State Machine, Turing Machine.

   (1995-03-13)