Heraldic and Vexillogical symbol in the form of a diagonal cross

A saltire is a diagonal cross used on flags and in heraldry. For example, the flag of Scotland (named St Andrew's cross) has a white saltire on a blue flag. The Union Jack (the flag of Britain) 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 St Patrick's cross).

White saltire in the flag of Gascony
A blue saltire of St Andrew is in the arms of the University of Edinburgh