XAU is the Currency code for gold ounces.

as of 22:23 Tue Apr 3 2001 server time, one XAU is worth:

1.0 XAU = 256.80 USD
1.0 XAU = 286.415 EUR
1.0 XAU = 32,243.74 JPY

I understand where they get the AU from, but how does X = Ounce?