A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical 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 Afro-Eurasia, the Americas or Eurasia as single continents. Zealandia, a largely submerged mass of continental crust, has also been described as a continent.