A beltway is a highway that encircles an urban area so that traffic does not have to go through that urban area. Other terms are "ring road" and "orbital motorway." Unlike urban highways, beltways generally require little or no demolition of existing property, as where possible they run through non-built up areas.
"The Beltway" as a proper noun typically refers to I-495, properly called "The Capital Beltway," the eastern half of which is also designated I-95. The Capital Beltway is a 6- to 10-lane highway which surrounds Washington DC. It loops through Suburban Maryland and Northern Virginia (and for a very short distance over the waters of the District of Columbia), crossing the Potomac River in two different locations. The American Legion Bridge and the Woodrow Wilson Bridge are choke-points for area traffic. 
Because the Beltway is a closed loop, the usual directional terminology used on other highways is ineffective in describing I-495. Thus, rather than traveling on North I-495 or East I-495, the two directions on the Beltway are called the "Inner Loop" and the "Outer Loop". Travelers on the Inner Loop of the Beltway move in a "clockwise" direction, while Outer Loop travelers travel the opposite direction. For a few miles on either side of the Wilson Bridge, each of the loops splits into local and express (through) roadways, for a total of four roadways called (from north to south) Inner Loop — Local, Inner Loop — Through, Outer Loop — Through, and Outer Loop — Local.
The Beltway is an extremely busy roadway, used by tourists, commuters and interstate travelers. During rush hour it is not uncommon for the Beltway to slow to thirty miles per hour or less due to the factors such as traffic volume, accidents or weather related delays. Indeed, it is the third most congested freeway in the United States.
The phrase "Inside the Beltway" refers to political matters related to the Capitol in Washington DC.  "Inside the Beltway" is also a regular column in the Washington Times. Most governmental agencies and buildings are located inside the Beltway in Maryland, DC or Virginia.
Orbital motorways in the United Kingdom
- "Beltway," from Dictionary.com
- "Woodrow Wilson Bridge," from Roads to the Future
- GPS study ranks Capital Beltway third worst for freeway congestion, The Washington Post, January 21, 2010