1856, American English, from land (n.) + slide (n.). Earlier was landslip, still preferred in Britain. Old English used eorðgebyrst in this sense; literally "earth-burst." In the political sense, landslide "lopsided electoral victory" is attested from 1888.
The rapid downward sliding of a mass of earth and rock. Landslides usually move over a confined area. Many kinds of events can trigger a landslide, such as the oversteepening of slopes by erosion associated with rivers, glaciers, or ocean waves; heavy snowmelt which saturates soil and rock; or earthquakes that lead to the failure of weak slopes.