Vigorish, or simply the vig, also known as juice, is the amount charged by an offshore sportsbook for taking a bet from a gambler.
Let's take a look at what would have happened if you had made ten bets of a $400 bankroll at one of your favorite online sportsbooks where the odds are -100 (no juice) instead of -110, here, the ten bets of $40 would now risk $40 to win $40.00. If a players assumes a win rate of 5.45 times, you win x $40.00 (+$221.80) and 4.55 times you lose x $40.00 (-$182.00) for a profit of $39.80 versus at -110 x 4.55 a net showing of $1.60 .
The juice matters a lot. If there was no juice, all you would have to do to make money is pick at 50.1 percent, which is essentially flipping a coin. With juice, however, you have to pick at a higher rate which makes it more challenging.