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

Actors

    A model for concurrency by Carl Hewitt.  Actors
   are autonomous and concurrent objects which execute
   asynchronously.  The Actor model provides flexible
   mechanisms for building parallel and distributed software
   systems.

   (http://osl.cs.uiuc.edu/).

   ["Laws for Communicating Parallel Processes", C. Hewitt et al,
   IFIP 77, pp. 987-992, N-H 1977].

   ["ACTORS: A Model of Concurrent Computation in Distributed
   Systems", Gul A. Agha , Cambridge Press, MA,
   1986].

   (1999-11-23)