haha, no biggie...
APO, without getting too detailed, is another term for a military overseas mailing address. Since all of our mail gets sent to one location (for us in Japan, our location is San Francisco, CA), we can only receive USPS mail. Once it gets to San Fran, it is then turned over to the military mailing system, and they carry it the rest of the way, wherever the end location is. Since UPS or FedEx wont send something that they cant carry all the way to the end address, USPS is all we can use over here. Evidently, there has been some changes to how you can mail packages via USPS now, since the seller says he can no longer support mailing stuff via USPS.
Sorry about the acronym! Us military types wouldnt be able to survive without using them! haha...