Australasia is a part of Oceania, or the same thing according to some. The consensus is that Australasia comprises Australia, New Zealand, the island of New Guinea and neighbouring islands north and east of Australia in the Pacific Ocean.
Oceania includes more Pacific islands than Australasia, such as Hawaii, Guam, Melanesia, French Polynesia, the Marquesas islands, the Cook Islands, the Samoas, Tonga and perhaps all Indonesia and Malaysia islands. See our Pacific Maps.
Oceania/ Australasia is usually considered to consist of three South Pacific regions– Micronesia, Melanesia and Polynesia (that is to say squillions of tiny coral atolls and volcanic islands, with small human populations) as well as Australia (the only continent involved), New Zealand, Papua New Guinea, East Timor, and Malaysia.