In the United States, the two major political parties are the Republicans and the Democrats. The terms are portmanteaus, or combinations, of the two party names. They are often applied to politicians who hold a mix of views from both political parties.
Historically, Republicans have tended to be pro-business and for more limited government, Democrats have tended to stand for more liberal social policies and an expanded role of government social services and regulations. In practice, due to their many similarities in philosophy and stated intentions for how to run the government, some commentators, such as right-wing Michael Savage, have opined on how it is often hard to tell the parties apart, leading to the terms' coinage. This was a view shared on the left by the Green Party during the 2000 U.S. Presidential election, whose bumper stickers read, "Bush and Gore make me wanna Ralph [Nader, the 2000 candidate.]"
See also Duverger's law.