We all know what a cross looks like, and yet when asked to describe one, the only valid answer is, "Which one?"
This page outlines a cross used in Christian art, with a heraldic name of Crux Decussata.
Decussata comes from decus, Latin for 'distinction', 'honour', 'glory' and 'grace'.
The Roman numeral 'X' has a value of ten (decem). The Chinese and Japanese character for ten also happens to be a cross: .
The origin of that East Asian character is usually, yet erroneously, explained as two lines crossing to symbolise the four main directions, which in turn expressed the concept of completeness and by association all the fingers, i.e. ten. However, this seems a confused version of its more likely origin; the depiction of a sewing needle with thread passing through the eye, and was used as a substitute for the more complex character , meaning 'hands together', i.e. ten fingers. (See also Fingers Crossed.)
Even so, the association with 'completeness' is carried over into the general meaning of the Christian cross, which was used to complete the mission of Jesus in the world 2,000 years ago.
The more common term for Crux Decussata, especially in a Christian context, is the St. Andrew's Cross