In a lottery draw, a rollover is a prize that includes the prize money from the previous draw, because nobody won it.
What does 10x rollover mean in sports betting? 10x states the number of times that you need to roll over your bonus. For example, if you've got aR$200 bonus then you will need to wagerR$2000 (10 xR$200 bonus) at the sportsbook to clear the bonus in full.