In politics, a "landslide" refers to an election in which one party's victory is overwhelming. Just as in any other sport, the only thing that matters in elections is who wins and loses, but a landslide victory can have added benefits, such as a coattail effect, and the fact that (if the position being run for is an executive one) it can give the winner a mandate, because their agenda was supported by a large number of voters.

What constitutes a "landslide" is not a precisely defined thing. Since elections are often played up for drama in the newsmedia, elections are defined as being landslides with around a 10% margin in the popular vote. Because of the electoral college system in the United States, and the parliamentary system in many other countries, an apparently greater landslide can occur in those numbers. In the electoral college system, for example, a 55% popular vote would probably translate into a 75% electoral college vote; and in a parliamentary system the ruling party may get a slight margin in a large number of districts, again giving a situation where 55% of the popular vote could turn into 75% of the districts.

I feel that the metaphor of a "landslide" can be somewhat misleading. In an actual avalanche, of course, the weight of the earth would be thousands of times greater than that what is buried, which is truly overwhelming. In a landslide in an election (at least in a modern Democracy), the margin of victory is usually around 10%. If there was a group of 20 people, and 11 of them felt one way, and 9 felt the other, it would hardly be considered an overwhelming tide of opinion. And yet, in elections, an 11-9 split would be considered quite an overwhelming majority.