

A saltire is a diagonal cross used on flags and in heraldry.
The flag of Scotland (named Saint Andrew's cross) has a white saltire on a blue flag.
The Union Jack (the flag of the United Kingdom) combines the flags of England, Wales, Scotland, and Ireland. These were the countries that belonged to the U.K. when the Union Jack was created. The Union Jack has two saltires of different colours: a white saltire copied from the flag of Scotland, and a red saltire taken from a flag of Ireland (named Saint Patrick's cross).