The continent; the principal land; -- opposed to island, or peninsula.

(noun) The single continent on the world containing the City of Atlantis. The continent itself extends to within 50 km of either magnetic pole, and encompasses roughly a quarter of the planet's surface.

The nearest large land to an island - Cornwall or the UK is the mainland for the Scilly Isles; Scotland is the mainland for the Orkneys.

the main land mass of a country or continent; as distinguished from an island or peninsula

Refers to the continental United States excluding Alaska and Hawaii.

the main part of land other than islands

Mainland is usually the continental part of a region, as opposed to the islands nearby. Sometimes the residents are called "the Mainlanders". As a result of the usually larger area of mainland, there are significantly more mainlanders than islanders, and mainlander culture and politics sometimes threaten to dominate those of the islands.