Heraldic cross
I believe the answer is:
'heraldic cross' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for saltire that I've seen before include "standard for Scots" , "Cross like St Andrew's" , "The Scottish flag" , "flag - 8's? [SAINT ANDREW]" , "Heraldic cross" .)