A saltire is an X-shaped figure in heraldry. It usually occupies the entire field in which it is placed.
A saltorel, or saltire couped, only occupies the middle part of the field, without extending to the edges.
A field that is party per saltire is divided into four areas in an x-shape. If two tinctures are specified, the first refers to the areas above and below the X, and the second refers to the ones on either side. Otherwise, each of the four divisions may be blazoned separately.
Charges blazoned as "in saltire" are arranged in an X-shaped pattern (obviously five or more are necessary for this to be feasible).
A saltire is used in the arms of Scotland, and the Scottish flag is a blue field with a white saltire; it represents Saint Andrew, the patron saint of Scotland, who is supposed to have been crucified on a cross of that shape. Because of its use in the Scottish arms and flag, the saltire appears in the Union Flag and the arms of Nova Scotia) The phrase "The saltire" is sometimes used in patriotic literature to refer to the Scottish flag.