Motus (singular motu; Polynesian for islet, islet) is the name given to the reef islands of an atoll that occur only in tropical waters. The term is used only in Polynesia. The tidal channels between the motus, which ensure the exchange of water in the lagoon, are called hoa.
The classic atoll consists of a volcanic central island surrounded by a coral reef with more or less numerous motus. They consist of coral debris and sand and usually rise only slightly above sea level. Motus are covered with palms or other tropical vegetation, islands without vegetation are usually called sandbars.
In terms of size, there is no exact demarcation. Some motus of large atolls, for example those of Rangiroa Atoll in the Tuamotu Archipelago, have an area of several square kilometres and are inhabited, on other motus there is only room for two or three coconut trees. The medium-sized motus of Bora Bora shown on the right have a diameter of about 300 m, of which about 200 m are covered with vegetation.