Definition from Wiktionary, the free dictionary
Proper noun 
- A group of islands off the northwest coast of mainland Europe, comprising Great Britain, Ireland, the Isle of Wight, the Isles of Scilly, the Isle of Man, the Outer Hebrides, the Inner Hebrides, the Orkney Islands, the Shetland Islands and many other smaller islands. Use may include the Channel Islands, although these are physically closer to mainland Europe.
Usage notes 
The term is sometimes seen as politically misleading or outdated, particularly in relation to Ireland.
a group of islands off the northwest coast of mainland Europe