An island is an isolated piece of land that is surrounded by a dramatically different habitat, such as water. The world of Poptropica consists of islands.
Description[]
Chunks of different areas and time periods appear as islands rising from the ocean through portals. Sometimes the islands sink back down and go back to their respective timelines, but as Jonas said, that rarely happens. (Interesting to note is that the only in-game island which has been shown sinking back down and coming back up repeatedly is Poptropolis Games Island).
Some of these islands are from Earth, or universes similar to Earth (Shrink Ray Island, Counterfeit Island, Spy Island), while others are from universes far different (Game Show Island, Steamworks Island, Goofball Island).