What common nickname is used for the United Kingdom's national flag?

The United Kingdom’s national flag is commonly nicknamed the Union Jack.

It is also called the Union Flag, and both names are accepted in modern usage. The design combines the red Cross of Saint George for England, the white Saltire of Saint Andrew for Scotland and the red Saltire of Saint Patrick for Ireland.

The present flag dates from 1801, when the Kingdom of Great Britain and the Kingdom of Ireland were united. Wales does not appear separately because Wales had already been incorporated into the Kingdom of England when the earlier union flag was created.

The word “Jack” originally referred to a small flag flown from a ship’s jackstaff, usually at the bow. The Union flag was used in that maritime position and gradually became known as the Union Jack. Although sometimes described as a naval-only term, historical usage and modern vexillological guidance accept it for the national flag generally.