The Union Jack or Union Flag is the national flag of the United Kingdom. The flag also has an official or semi-official status in some other Commonwealth realms i.e. a ceremonial flag in Canada.
It contains three crossed
1. Cross of Saint Andrew
2. Cross of Saint Patrick
3. Cross of Saint George.
Flag represents regal union between England and Scotland of 1606 according to which the flag of England (a red cross on a white background, known as St George's Cross), and the flag of Scotland (a white saltire on a blue background, known as the Saltire or St Andrew's Cross), would be joined together, forming the flag of England and Scotland for maritime purposes. And union of Great Britain and Ireland in 1801 where it combined with the red saltire of St Patrick to represent Ireland.