Great Britain vs. United Kingdom

What is the difference between Great Britain and United Kingdom. What islands are part of UK? How is island different from isle?

Great Britain is a geographic location. It is the largest island of the United Kingdom that is is a country. It includes England, Scotland without its islands, and Wales.
This is the ninth island in the world for its size and the third for its population.
Politically, it is a territory of the United Kingdom of Great Britain and Northern Ireland.
The term Britannia Major in Latin has been used to distinguish it from Britannia minor that is a part of France.

The UK (United Kingdom) as shown in the map also includes Northern Ireland, the Hebrides, part of Scotland.

The Channel Islands, Jersey and Guenersey mainly, as the Isle of Man are dependencies of the crown but are not part of the United Kingdom or Europe.

The British consider that the word Britain is a shorthand for the United Kingdom.

British Islands or Isles

Another useful distinction is to be made between:

Island or isle

An island is a geographical location (land surrounded by water too small to be a continent), is translated into English by island or island as usual. Originally island is a contraction of island-land, but no real difference now except that island is an island and more formal language more poetic.
Iceland has Ísland (ground ice), English Iceland, and seems to have no connection with the word island.

England is the translation from England who just Angleland, the country of the Angles, a Germanic tribe that invaded the country in the 5th century.
Britain comes from the name of the Celtic tribe that lived Brython the territory before.

Éire or Ireland

Éire is an Irish name for both Ireland and the Republic of Ireland. Actually the Irish do not make a difference between Ireland the whole isle, and their country, they name Ireland the country.

Maps

Map of the World

Data about any country.