beltway

Short definition from Wiktionary

Noun

1. 1
   A freeway that encircles a city.

Proper noun

1. 1
   A 64-mile Interstate freeway surrounding Washington, D.C.
2. 2
   The expressway that surrounds another city.
3. 3
   The US federal government and policy and lobbying organizations, located in Washington, D.C.

Adjective

1. 1
   Of or relating to the culture of Washington, D.C.; politicized.