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.
Realm
More broadly, a "realm" may encompass territories that are subject to a monarch, yet are not a physical part of his or her "kingdom"; for example, the Cook Islands and Niue are considered parts of the Realm of New Zealand, although they are not part of New Zealand proper.