A mechanism limiting the exchange of information between information systems or subsystems.
NIST SP 800-53 Rev. 4 under Guard (System)
(CNSSI 4009 - Adapted)
A computer system that (a) acts as gateway between two information systems operating under different security policies and (b) is trusted to mediate information data transfers between the two.
See transfer cross domain solution.
(IETF RFC 4949 Ver 2)