The Collaborative International Dictionary of English v.0.48:

Oceania \Oceania\ prop. n.
   A large group of islands in the south Pacific sometimes
   including Australasia and the Malay Archipelago.

   Syn: Oceanica.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Oceania
    n 1: a large group of islands in the south Pacific including
         Melanesia and Micronesia and Polynesia (and sometimes
         Australasia and the Malay Archipelago) [syn: Oceania,
         Oceanica]