Why is the UK flag called Union Jack?

Related questions

1. Is it illegal to fly the Union Jack in the UK?
2. Do I write England or United Kingdom on letter?
3. When did UK become UK?
4. What's the difference between the English flag and the British flag?
5. Does England own Scotland?
6. What is the real flag of England?
7. What is England if not a country?
8. Why is the British flag in the Hawaiian flag?
9. Why is Wales not on Union Jack?
10. What was England called before England?

Tags

1. #referred
2. #incorporate
3. #ireland
4. #because
5. #incorporated
6. #patrick
7. #wondering
8. #already
9. #british
10. #cross
11. #amended
12. #principality
13. #union
14. #england
15. #never
16. #welsh