A safe district is a voting region in which the clear majority of voters are members of, or overwhelmingly favor a single political party. This makes incumbent representatives for those regions very difficult to beat in elections.
Congressional terms are meant to be limited. Although re-election is permitted, Congress is designed to turn over a percentage of its seats every two years for the House of Representatives and every six years for the Senate. According to James Madison, one of the founding fathers, term limits were not included in the Constitution because the men who structured the U.S. government wanted to leave room for those elected members of Congress who were extraordinary to continue to serve.
In recent years, however, frustrated voters have begun to push for congressional term limits, claiming that safe districts are the reason for the stalemating that has been occurring in Congress. The idea of term limits is not new, and although they have never been law on a federal level, nearly half of all individual states imposed them at some point, until the U.S. Supreme Court ruled that it was unconstitutional to do so in the case of U.S. Term Limits, Inc. versus Thornton in the mid 1990s. To skirt such laws, many states have begun redrawing district lines to redistribute voters more evenly amongst the parties.