Term used when prize money that isn't won or claimed is available for another round (8)
I believe the answer is:
rollover
(Other definitions for rollover that I've seen before include "Turn turtle (as a jackpot might do?)" , "Turn in bed; allow (debt) to continue" , "Prize money taken forward" , "Chance for an even bigger Lotto jackpot" , "result if no winner?" .)