iron triangle

Short definition from Wiktionary

Noun

1. 1
   The policy-making relationship among the congressional committees, the bureaucracy (executive, sometimes called “government agencies”), and interest groups or lobbyists.
2. 2
   Any self-reinforcing power structure, whether intentional or accidental, formal or informal.

Proper noun

1. 1
   A key communist Chinese and North Korean concentration area and communications junction during the Korean War, located in the central sector.
2. 2
   A stronghold of the Viet Minh during the Vietnam War, located north of Saigon.
3. 3
   Alternative letter-case form of iron triangle.