From YPPedia

An atoll is a mini-island that can only be reached via a buried treasure expedition. Once a ship reaches the atoll, players disembark and begin searching for buried treasure which is recovered through the foraging puzzle. The island design team was tasked with creating the many and varied atolls - two new designers were brought in from the Beat the Champs contest to help meet the deadline.

See also

List of known atoll words