Island
An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island in a river or a lake island may be called an eyot or ait, and a small island off the coast may be called a holm. A grouping of geographically or geologically related islands is called an archipelago, such as the Philippines.
Orkney
The other islands in the group are classified as north or south of the Mainland. Exceptions are the remote islets of Sule Skerry and Sule Stack, which lie west of the archipelago, but form part of Orkney for local government purposes. In island names, the suffix "a" or "ay" represents the Norse "ey", meaning "island". Those described as "holms" are very small.