Definition - What does Oceanic Islands mean?
Oceanic islands are islands that rise from the ocean floor due to seismic or volcanic activity, as opposed to islands which form as part of a continental shelf where the water is shallow. Oceanic islands form far away from continents and are not linked with any large land masses. They can be found alone or in groups surrounded by deep water on all sides.
Safeopedia explains Oceanic Islands
Oceanic islands form as land is pushed up to the surface of water as in the case of a volcano or other seismic activity that pushes land upward. To start with, the land is often uninhabitable due to vocalic activity, but, as this cools, life starts to appear on the island. Barrier reefs often appear after water erosion takes place and the centre of the island sinks, while coral at the edges grows.