(American) a highway that runs around the border of an urban area;
e.g. If you want to avoid the traffic in a city, you might use the beltway and drive around the city instead of through it.
(noun)
(American) the city of Washington D.C., especially its social and political sphere, used to represent how exclusive or narrow its view is perceived to be (usually used as "Beltway");
e.g. Your ideas might be appropriate in the Beltway, but they won't work anywhere else.