The contiguous United States are the 48 U.S. states on the continent of North America that are south of Canada, plus the District of Columbia. The term excludes the states of Alaska and Hawaii, and all off-shore U.S. territories and possessions, such as Puerto Rico.
Together, the 48 contiguous states and D.C. have an area of 3,119,884.69 square miles (8,080,464.25 km²). Of this, 2,959,064.44 sq mi (7,663,941.71 km²) is land, comprising 83.65% of U.S. land area. Officially, 160,820.25 sq mi (416,522.38 km²) is water area, comprising 62.66% of the nation's water area. Its 2000 census population was 279,583,437, comprising 99.35% of the nation's population. Its population density was 94.484 inhabitants/sq mi (36.480/km²), compared to 79.555/sq mi (30.716/km²) for the nation as a whole.
While coterminous U.S. and conterminous U.S. have the same precise meaning as contiguous U.S., other terms commonly used to describe the 48 contiguous states have a greater degree of ambiguity.
Because Alaska is also on the North American continent, the term continental United States, if interpreted literally, should also include that state, so the term is sometimes qualified with the explicit inclusion or exclusion of Alaska to resolve any ambiguity. The term was in use prior to the admission of Alaska and Hawaii as states of the United States, and at that time usually excluded outlying territories of the U.S. However, even before Alaska became a state, it was sometimes included within the "Continental US".
CONUS, a technical term used by the U.S. Department of Defense and General Services Administration, has been defined both as the continental United States, and as the 48 contiguous states. The District of Columbia is not always specifically mentioned as being part of CONUS. OCONUS is the same term with addition of O for outside, thus Outside of Contiguous United States (OCONUS).
The term lower 48 may or may not include the District of Columbia (which is not part of any of the 48 states). The National Geographic style guide recommends the use of contiguous or conterminous United States instead of lower 48 when the 48 states are meant, unless used in the context of Alaska. Otherwise it is avoided as a misnomer, because the entire state of Hawaii is further south than the most southern point of all the continental states.
Both Alaska and Hawaii, because of their own location relative to the contiguous United States, have their own unique labels for it.
Alaska became the 49th state of the United States on January 3, 1959. Alaska is on the northwest end of the North American continent, but separated from the rest of the United States by Canada. In Alaska, given the ambiguity surrounding the usage of continental, the term "continental United States" is almost unheard of when referring to the contiguous 48 states. Several other terms have been used over the years. The term Lower 48 was for many years the most common Alaskan equivalent for "contiguous United States". However, since the 1980s Alaskans have increasingly adopted the term Outside to refer to the rest of the United States. Alaskans will speak of going Outside to vacation or will refer to being born Outside.
Hawaii became the 50th state of the United States on August 21, 1959. The Hawaiian Islands are located in Oceania and are about from the North American mainland. In Hawaii and overseas American territories, for instance, the terms the Mainland or U.S. Mainland are used to refer to the continental United States. Visitors to Hawaii sometimes refer to the continental States as "the States", but this is considered naïve or offensive to local residents.
Some parts of the contiguous United States are accessible by road only by travelling on Canadian soil. Point Roberts, Washington, Elm Point, Minnesota, and the Northwest Angle in Minnesota are three such places. Alburgh (town), Vermont is not directly connected by land, but is accessible by road via bridges from New York and Vermont.