An island continent is an entire continent that is completely surrounded by water. Australia is an island continent.
It was known as the Dark Continent in the past.
Africa used to be known as the Dark Continent. This is because nothing was known about the interior of Africa up until about the mid 1800s. So to the outside world, interior Africa was known as dark and mysterious.
The dark continent is a 19th century expression to describe Africa
People from Europe, Australia, and the Americas used to call Africa the "dark continent." There were two reasons. One, was that it was very difficult for explorers who went there, and many of them died of illnesses such as yellow fever and malaria. Second, was because most of the continent was unknown as a result of that difficulty in exploration.