Spread – also known as the line or point spread, it is generally thought of as the predicted margin of victory for one team. In reality, it's a number chosen by the oddsmaker that he feels will encourage an equal number of people to wager on the football underdog and the pigskin favorite. The negative value -13.5 indicates that team is favored by 13.5 points. The positive value +13.5 indicates that team is the underdog by 13.5 points. Betting on the favorite means the team must win by at least fourteen points to cover the spread. The underdog team can lose by thirteen points and still cover the spread.
Point Spread – This is the margin of victory for a game determined by the oddsmaker. Sportsbooks use this to create action on both teams. The favorite will have to win by more than the margin the oddsmakers set. If the Broncos are favored by 2.5 against the 49ers, they must win by 3 points or more for a win. If they only win by 2, they didn’t cover the spread and those who bet the 49ers will win.
For the player who wagers on San Francisco -5, San Fran must win by more than 5 points for this to be a winning bet. For the player who wagers on St. Louis +5, they must either win the game or lose by less than 5 points for this to be a winning bet. If the outcome falls on the number, the bet is declared a “Push” and your original stake amount gets refunded.

But what if the basement-dweller team was spotted 24 points? That's the concept behind the point spread. When two teams meet on the football field or a basketball court, one team is typically better than the other. If all bettors had to do was to pick the winning team, everybody would simply wager on the best team and collect their money. Gambling institutions, sportsbooks, and bookies would soon go broke. 
In general, the betting public tends to gravitate towards favorites when betting the games regardless of the actual pointspread. This is especially true with high-profile teams such as Dallas and Green Bay in the NFL and Golden State and Cleveland in the NBA. The sportsbooks are well aware of this phenomenon and often times they will adjust the betting spreads accordingly. This, in turn, actually adds some value to the underdog when you consider that a pointspread is nothing more than a handicapping tool that is designed to even out the match.
Point Spread: The point spread remains the favorite way to wager on pro football, regardless of how many new forms of wagering come on stream. It’s called the line or spread and it’s known as betting ‘sides.’ The common misconception is that Las Vegas sets the spread as its best guess at the margin of victory. But really, it's a number they feel that is a perfect balance and will see an equal number of people to bet the underdog as on the favorite. A negative value like -6.5 means that team is favored by 6.5 points. So deduct 6.5 points from their total score. A positive value on the same game would be +6.5 (add 6.5 points to their final score) and would make that team an underdog of 6.5 points. The favorite must win by at least seven points to cover the spread. The underdog can lose by six points and still cover.