请问高手这个付款方式是什么意思？

hello jack, we would like to make another purchase of am tags order quantity will be 50,000. delivery:? ???10,000 -??april 20, 2013 10,000 -??may 17, 2013 10,000 -??june 14, 2013 10,000 -??july 26, 2013 10,000 -??aug. 23, 2013 we would like to purchase these on open account, net 30 day. can you accommodate us on this? 客人之前找我们下蛋都是100%前t/t的，现在他说要 open account, net 30 days. 请问这是什么意思？是不是到货以后30天内才付款？