This option is most commonly associated with football (soccer), although it can be applied to other sports as well, such as basketball or hockey. The "1.5" in "Over 1.5" represents the minimum number of goals or points that must be scored for your bet to be successful.
To calculate your potential payout on an underdog, all you need to do is multiply your stakes (the amount of money you wagered) by the value resulting from the moneyline odds divided by 100. Put simply: Potential profit = Wager x (Odds/100).