Source : Free On-Line Dictionary of Computing

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 {platform}s.
     
        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)