A parlay is a wager that involves two or more events. For example, I'll bet you that I can get my golf ball onto the green from the tee in two shots, then hole it in two (more) shots. To win, I have to be successful in both propositions (and I have to win as specified -- I can't get onto the green in one shot and sink the ball in three, or get on in three and sink it in one).
Parlay is also a verb. When you parlay, you use the winnings from one bet to make another wager.
You can create and bet parlays in a sports book by combining wagers "off the board," or by using a parlay card, which is (usually) a rectangular piece of thin card stock pre-printed with the eligible betting options that you are allowed to combine. For example, a football parlay card might have bets on sides, totals, and perhaps some propositions.
The attraction of parlay cards to players is the big payoffs they offer for small bets -- 10-teamers, for example, might pay 850-to-1. But they're no gambling bargain. Parlay cards in Nevada sports books require at least three bets and pay winners at odds in the area of 6.5-for-1 (which is the same as 5.5-to-1). The fair payoff for correctly predicting three independent events is 7-1, so a sports book ostensibly has an 18.75% edge on this play. Why "ostensibly"? Because the pre-printing of the pointspreads can yield opportunities when the current line moves away from the line on the card and players can lock in a number that's better than what they should be getting. Also, skilled gamblers sometimes find correlations in the betting options, which can also erase the book's advantage. For the most part, though, the casinos have a big edge on parlay cards and continue to profit handily from them every year.
One great parlay play is the free $5 parlay card offered on the NFL each week at the Hard Rock. You can choose a 4-, 5-, 6-, or 7-team parlay, which yields the following payoffs.
Parlay.........Pays 4 teams.......$50 5 teams......$100 6 teams......$210 7 teams......$395
The more teams you parlay, the less frequently you'll win, but your expected profit is a little more than $3 on this play -- plus there's no risk and you can make a decent score when you hit. You have to join HR's players club to be eligible.