(verb)
to make arrangements to stake the winnings of one bet on a successive bet, and especially to win such a series of bets and thus to turn the initial stake/winnings into a greater amount;
e.g. She attempted to parlay what money she had in the casino in the hopes of winning a large sum.
(verb)
in informal usage, to increase the value of something or to transform it into something of much greater value, or to successfully take advantage of something;
e.g. He plans to parlay his skills and climb the ladder to a successful career.