A Moneyline bet is a wager on which team will win the game, including extra innings if they're played. The minus odds indicate the favorite, and the plus odds indicate the underdog.
For example: the Toronto Blue Jays are the favorite at -120, and the Detroit Tigers are the underdog at +100. A $100 bet on the Blue Jays returns $183.33 total if they win. A $100 bet on the Tigers returns $200 total.