Australia is the smallest of the geographic continents, though not of geological continents. There is no universally accepted definition of the word "continent"; the lay definition is "One of the main continuous bodies of land on the earth's surface." (Oxford English Dictionary). By that definition, the continent of Australia includes only the Australian mainland, and not nearby islands such as Tasmania or New Guinea. From the perspective of geology or physical geography, however, a "continent" may be understood to include the continental shelf (the submerged adjacent area) and the islands on the shelf, which are taken to be structurally part of the continent. By that definition Tasmania, New Guinea and other nearby islands such as (Aru Islands and Raja Ampat Islands) are part of the Australian continent, also known as Sahul, since they are part of the same geological landmass. These islands are separated by seas overlying the continental shelf — the Arafura Sea and Torres Strait between Australia and New Guinea, and Bass Strait between mainland Australia and Tasmania.