The Union Jack is the national flag of the United Kingdomm of Great Britain and Northern Ireland. The design of the Union Jack combines aspects of three older national flags: the red cross of St George of England, the white saltire of St Andrew for Scotland and the red saltire of St Patrick to represent Ireland. Wales, despite also being part of the Union, has never been represented on the flag. Photo: allaboutyou.com
Great Britain is the official name given to the two kingdoms of England and Scotland, and the principality of Wales. The United Kingdom (UK) includes these areas as well as Northern Ireland. Britain refers to only England and Wales, though some will shorten Great Britain with this term.