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.
Wh-movement
However, there are cases in which this is not possible. Certain kinds of phrases do not seem to allow a gap. The phrases from which a wh-word cannot be extracted are referred to as "extraction islands" or simply "islands". The following subsections briefly consider seven types of islands: 1) adjunct islands, 2) wh-islands, 3) subject islands, 4) left branch islands, 5) coordinate structure islands, 6) complex NP islands, and 7) non-bridge islands. These island types were all originally identified in Ross' seminal dissertation. The islands in the examples that follow are underlined in the a-sentences.