islet

An islet is a small island, typically smaller than what is commonly called an island. The term islet is used in geographical contexts to refer to minor, often uninhabited landmasses that rise above sea level and are surrounded by water. The word islet derives from the French islette, a diminutive of ile (island), ultimately from Latin insula.

In biology, islet or islets of Langerhans are clusters of endocrine cells in the pancreas. They are dispersed throughout the exocrine tissue and regulate blood glucose by producing hormones such as insulin, glucagon, somatostatin, and pancreatic polypeptide. They vary in size and number by species and health status; in humans there are about one to two million islets. They are richly vascularized, enabling rapid hormone release in response to blood glucose levels. Damage to these islets underlies certain forms of diabetes mellitus.

Geographically, islets appear in many coastlines and archipelagos, from tropical to temperate regions. They are often small, may be uninhabited, and can serve as habitats for seabirds, shorebirds, and marine life. Islets can be important for navigation and ecology, and many have been designated as protected areas to conserve wildlife and habitat.

Etymology and usage notes: the term emphasizes small size relative to larger islands and is used across disciplines, from cartography to biology. In some contexts, “islet” may be used interchangeably with other small-island terms such as cay or keys, though definitions vary by region.