I believe it's their zip code. What I always do with foreign addresses is copy and paste their address from their PayPal invoice to a shipping label. So if the package were to get lost in the mail it wouldn't be much of my responsibility since the address they gave me is exactly what's on the shipping label.
Also, in case you didn't know yet... If you are mailing out only 2-3 cds to a foreign country, you don't need no customs form on the package. The only countries I've encountered that are strict on having customs form on every package are Canada, Germany, Mexico, and Australia.
BTW, what's the oddest country you've ever sent a CD to?? Just the other day I sent a package to Johannesburg, South Africa!! Shit is crazy!!!!! I hope it gets there!