It means that if you transfer $100, you would have to give the Greek $400 in play before you can withdraw it or move it. Strange policy considering they are sister books.
Greek, BetJam, WSEX, Matchbook, no fees for book to book transfer.
Minimum transfer, I believe is $500, but they don't all do transfers with the same books. Bookmaker discourages it, they have a minimum fee of $100. Best way to find out details call em and ask them.