simply means you can bet with money that is tied up in a current wager, as long as that wager wins...
you have 110.00 on Duke to win....you can them bet up to 210.00 on another bet, saying "if" duke wins, i want 150.00 on north carolina.......you can also bet if win/push, but then you will be limited to the 110.00 of the original wager, since a push would only put 110 back in your acct...
once duke wins, then you would have 60 in your acct, and a new wager on NC for 150.00.......if Duke loses, then everything is done....