Applying to everyone or everything in a particular group without exception. It means universal application or affecting all categories equally.
This phrase comes from horse racing, where the 'board' displayed the odds for win, place, and show bets. A bet 'across the board' meant wagering on the same horse to win, place, and show - covering all possibilities.
The racing origin explains why the phrase suggests comprehensive coverage rather than random distribution. Gamblers who bet 'across the board' were hedging their bets to ensure some return regardless of their horse's exact finishing position, which mirrors how we use the phrase today to mean complete or universal coverage.
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