The Union Jack also known as the Union Flag, is the national flag of the United Kingdom. It is the British flag.
It is called the Union Flag because it symbolises the union of the countries of the United Kingdom. It is made up up of the individual Flags of three of the Kingdom’s countries all united under one Sovereign – the countries of ‘England, of ‘Scotland’ and of ‘Northern Ireland’. As Wales is not a Kingdom but a Principality it is not included on the flag.