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

De-Militarised Zone
DMZ

    (DMZ) (From the military term for an area between
   two opponents where fighting is prevented) DMZ Ethernets
   connect networks and computers controlled by different bodies.
   They may be external or internal.  External DMZ Ethernets link
   regional networks with routers to internal networks.
   Internal DMZ Ethernets link local nodes with routers to the
   regional networks.

   Compare red zone.

   (1995-02-23)