Pointspread betting or Puckline (hockey) betting is where the sportsbook decides on a margin of victory for the favorite that will make either team an attractive betting proposition.
On a Pointspread, your selection has to win by more than a specified score (or lose by less than a specified score).
Green Bay Packers -3.0
If you select 'Green Bay Packers - 3.0', the Packers must win the game by more than 3 points.
Dallas Cowboys +3.0
If you select 'Dallas Cowboys + 3.0', the Cowboys must win the game or they can lose, but only lose by less than 3 points.
If the score of the game ends in a difference of points that is equal to the point spread, your selection will be marked as a void/push.
Dallas Cowboys +3.0 vs Green Bay Packers -3.0, if the score is 20-17, the difference of score is 3, therefore wagers on both Dallas and Green Bay pointspreads are marked as a push.