Saint Andrew's Cross

Saint Andrew's cross is a cross shaped like the letter X.
It is called so because Saint Andrew, one of the twelve apostles of Jesus, is reputed to have been crucified on a cross of this shape.
The St. Andrew's Cross is not unique to the Confederate battle flag. The reason that the CSA put the St. Andrew's Cross on its flag is the Scottish heritage of the South.
The Scottish national flag has the St. Andrew's Cross in white on a field of blue.
It is also called the Saltire, the Boundary Cross and the crux decussata. Saint Andrew is believed to have suffered a martyr's death on such a cross, hence its name. The cross does not have to be at this particular angle to qualify as a saltire; the symbol X can also be considered a St. Andrew's Cross.