If you parlay a bet, then you take the winnings from one bet and bet it again on something else. You might have seen a gambler on TV parlay her winnings into a huge fortune.
The verb parlay is often used to talk about gambling, but it can be used more broadly to describe any initial stake that you turn into something much larger. You might parlay your early investment in your brother’s company into a high-paying leadership role. Parlay also has a noun form that describes these kinds of transactions. You might notice your Uncle Bob once again betting a baseball parlay.