A jackpot is a pile of money won during a game such as a poker. It's also any example of good fortune.
Originally, a jackpot was a pile of money in poker that accumulated until someone produced a pair of jacks (or something better). These days, a jackpot is any kind of prize, winnings, or success. If you get a high-paying job, you hit the jackpot. If you married a wonderful person, you hit the jackpot. Sometimes a jackpot is specific to a game, like the money won from a hand of 21, but any good fortune can be considered a jackpot.