A continent is one of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven regions are: Asia, Africa, North America, South America, Antarctica, Europe, and Australia. Variations with fewer continents may merge some of these, for example some systems include Eurasia or America as single continents.
Geologically, the continents correspond to areas of continental crust that are found on the continental plates, but include continental fragments such as Madagascar that are not commonly referred to as continents while others are largely covered with water, such as Zealandia. Continental crust is only known to exist on Earth.
Oceanic islands are frequently grouped with a neighbouring continent to divide all the world's land into regions. Under this scheme, most of the island countries and territories in the Pacific Ocean are grouped together with the continent of Australia to form a region called Oceania.