For any game in which you can bet on a winner, you can also bet on the total number of points scored. Called “game total” betting, sportsbooks will set a number at the total (like 42.5 for an NFL game) and you can bet over or under. If the number of points exceeds the total, the over wins.
Total bets are also a popular way to present props, like: “How many points will LeBron James score in Game 1 of the NBA Finals: over/under 29.5.”
Whenever you hear someone say they “have the over,” they are expecting a higher number for an event than bookmakers have set. The over is a far more popular bet for beginners since you are cheering for scoring, rather than the absence of scoring. But the under is often the best play, so be sure you think critically.