Sports betting companies make money by collecting a commission on losing bets, which is often called the vigorish.
Vig, or vigorish, is the cut or amount charged by a sportsbook for taking a bet, also known as juice in slang terms. The sportsbook only collects the vig if the bettor loses the wager.
For example, a point spread is often listed with -110 odds. If the Eagles are -6.5 point favorites, that would be at -110 odds. If there was no vig, it would be at even odds, or +100. With the vig, a $100 bet would result in a $190 payout. If there was no vig, a $100 bet would result in a $200 payout.
If you want to win $100 at -110 odds, you'd have to bet $110 because of the vig and when the bet loses, that $10 goes straight to the sportsbook. Without the vig, you could win $100 on a $100 bet.
Of course, not all sportsbooks are the same and sometimes regular odds are listed at -115 or -120. As more states legalize sports betting, the variety in vigs across states will be a talking point. That's because a lot of in-person sportsbooks take a higher cut of bets than online sportsbooks, who receive more bets because they are more widely accessible. While each state has different rules, there are certain states where sportsbooks have a higher vig across the board, no matter where you wager.
There are also situations where -110 odds would push to -120 or higher because that bet is getting a lot of money. If a lot of people are betting the Eagles at -6.5 (public money) and the sportsbook doesn't want to move that number to -7, they'll push the odds to -120 or -130, meaning a $100 bet would result in an even smaller payout.