iron curtain

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The military, political, and ideological barrier established between the Soviet bloc and western Europe from 1945 to 1990.
2. n. A barrier that prevents free exchange of ideas and information: "That department and the editorial department are separated by an almost impenetrable iron curtain” ( Brendan Gill).

Wiktionary

1. n. A barrier made of iron in the theatre, lowered between the stage and the auditorium for safety or to prevent communication.
2. n. idiomatic Any impenetrable barrier.

WordNet 3.0

1. n. an impenetrable barrier to communication or information especially as imposed by rigid censorship and secrecy; used by Winston Churchill in 1946 to describe the demarcation between democratic and communist countries