Safe seat

A safe seat is a political office for which one party holds a nearly insurmountable advantage in elections.

Sometimes the advantage is due to gerrymandering, but it can also be due to other factors such as demographics.

Examples of safe seats include the California 12th Congressional District (the one held by Nancy Pelosi, it has been Democratic since 1949), and the Tennessee 2nd Congressional District (which has, notwithstanding the switch between Republican and Democrat parties in the South, been held by Republicans since 1859, before the Civil War).

The opposite of a safe seat is a "swing seat."