A moneyline bet in sports refers to a wager on the winning team. The biggest difference between a moneyline bet and a spread bet is that the former doesn't involve points.
For example, the Philadelphia Eagles are a -6 point favorite over the New York Giants, but that number doesn't matter for the moneyline. The other part of the odds is that the Eagles are a -150 favorite to win, whereas the Giants are a +180 underdog to win. A moneyline bet would be a bet on -150 or +180. If you bet $100 on the Eagles to win at -150, you would net a payout of $166.70. If you bet on the Giants to win at +180, the payout would be $280 because they are an underdog.
In most cases, the favorite will have a " - " in front of its moneyline odds while the underdog will always have a "+ ." There are some cases in which the favorite is barely expected to win, often in a sport like soccer, where both teams will have a " + " in front of their moneyline odds. That's more often the case in soccer since draws are a possibility, whereas a winner is declared in almost every other sport because of overtime rules.