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

Object Request Broker
ORB

    (ORB) Part of the OMG CORBA specification,
   an ORB's basic function is to pass method invocation
   requests to the correct objects and return the results to
   the caller.

   To achieve this the ORB must be able must be able to identify
   and locate objects, handle connections from invoker and the
   data returned from methods.  Communication between the ORB and
   applications are achieved through IDL stubs and skeletons
   whilst the OMG has specified IIOP as the protocol through
   which ORBs may communicate with each other.  Using IIOP, an
   ORB may request method invocations from a remote object.

   (2003-11-21)