The Union Jack is not only the flag of the United Kingdom, it also features on numerous country's flags as well as the American stste of Hawaii and some Australian states and Canadian provinces.

The Union Jack flag is one of the most famous flags or icons in the world. It can be found represented on many other country's flags particularly Commonwealth countries and states and prvinces within those countries. Some of the most famous examples are the flags of australia, New Zealand and Hawaii.
The first idea of a flag for Britain was instituted by King James I in 1606. It was known variously as the British Flag or the Flag of Britain but by the 1670's it was formally called His Majesty's Jack or informally as the Union Jack.