The money line is a common form of sports betting. Unlike a spread bet, a bettor will simply pick one of the two teams to win a particular game, matchup, or tournament; and receive odds based upon how favored or unfavored they were to win.

Quotes

For the purpose of this articles, all prices will be quoted in US Dollars. Sportsbooks will list a money line as a + or -, followed by a dollar amount (which will be higher than 100). The - indicates that a team is favored to win, and so the bettor must wager that dollar amount to win 100 dollars. The + indicates that the team is not favored to win, and so the bettor can wager 100 dollars to win the amount. For example, in Super Bowl XXXIX:

• The New England Patriots were favored to win, and the money line was roughly -265. To make this bet, a bettor would have to pay the sportsbook $265, and could stand to collect $365 (a $100 profit).
• The Philadelphia Eagles were not favored to win, and the money line was roughly +245. To make this bet, a bettor would have to pay the sportsbook $100, and could stand to collect $345 (a $245 profit).

Sources

As each casino runs an independent sportsbook, these money lines can vary from place to place. Theoretically, a bettor could capitalize on differences between differing sportsbook for an arbitrage opportunity. However, this is highly unlikely.