The phrase across the board often refers to an all-encompassing action, one that affects the entire spectrum of a group. For example, a company may decide to give all employees a 10% raise in salary. It would be fair to characterize this sweeping action as an across the board raise. When an event is described in this way, there are no exceptions — everything is affected equally.
The origin of the phrase is a bit murky. Some sources suggest that the term originated with the first organized stock markets in New York City. Individual stock actions were manually entered on large chalkboards placed along the walls. Any major adjustments which affected all of the stocks would have to be implemented by hand "across the board," so to speak. When stockbrokers spoke of sweeping changes in this way, they were referring to the flurry of activity surrounding these tally boards.
Another theory is that the phrase originally referred to a betting method in horse racing. Standard betting on horse races allows bettors to place wagers on individual horses or a combination of horses. A horse is considered a winner if it places first (win), second (place), or third (show). Additional bets can be placed on a group of two or three horses, often called a perfecta or trifecta bet.
There is one other betting option available. The same horse can be picked to win, place or show. This is sometimes called an across the board bet. The bettor essentially covers his potential losses by betting on all possible outcomes.
The phrase can also be hyphenated, such as an across-the-board reduction in salaries. Some may refer to a reform of political leaders or an examination of a company's policies in this way. The implication is that all elements of the group would receive unbiased attention, and that any changes would be implemented equally.