The flag is normally called Union Jack” because it represents a union of countries: England, Ireland, and Scotland. The Waless flag does not include because Wales was never ruled in the same way that the other countries.
Actually it shouldnt called the Union Jack”, because a jack is a flag that is flown on the back of a naval ship. Its called the Union Flag”.
The Union Jack includes the Cross of St. George (England), the Cross of St. Andrew (Scotland) and the cross of St. Patrick (Ireland).
The Union Jack is the most important of all British symbols, and it is flown by representatives of the United Kingdom all over the world.