In sports betting the closing line refers to the final odds available at the time the betting market for a given event closes. These are the last lines being offered by a sportsbook before the match begins.
Experienced sports bettors consider the closing line to be when the market is at it's highest expected efficiency. Oddsmakers shape their lines using the early wagers of knowledgeable sports bettors who have identified a betting advantage. Opening lines are adjusted and move towards the market's expected value. As a result the longer a betting market is open the higher it's efficiency. This yields closing lines which do not have betting edge on either side. Sports bettors are advised to bet into opening lines in order to have the largest potential betting advantage.
Bettors who can consistently beat the closing line often find long term success.