A totals bet, commonly known as an over/under bet, involves betting on the combined score of both teams in a game. Bookmakers set a predicted total score for the game, and bettors choose whether they think the actual combined score will surpass (over) or fall short of (under) that number.
An over/under in sports betting is a bet on the total number of points in a game. It's often called "the total." You're wagering on whether or not the combined points/goals/runs scored by both teams will go over or under a predetermined amount.