Across the board (PW)
including everyone or everything
The company had a successful year. All salaries were increased by 10% across the board.
(MW)
1: placed to win if a competitor wins, places, or shows
2: embracing or affecting all classes or categories: blanket
(UsingEnglish.com)
If something applies to everybody, it applies across the board.
(thePhraseFinder)
Meaning
Embracing all classes or categories without exception.
Origin
The words 'across' and 'board' are of course commonplace in English and so it isn't difficult to imagine them being combined by chance to form 'on the board' in everyday speech and in literature. There are many early examples of the phrase in the context of people talking to each other across a table (a.k.a. board) or when playing board games. Those situations aren't the source of the phrase though - the boards that were being referred to when the phrase was first used to mean 'encompassing all aspects' were those used by bookmakers to mark up the odds in races. An 'across the board' wager is one in which equal amounts are bet on the same contestant to win, place, or show.
The phrase was coined in America and the earliest example of it that I can find is from The Atlanta Constitution, November 1901:
"Cousin Jess won the steeplechase after a hard drive in the stretch, lowering the best previous time of 4 09 by seven seconds. Dr Einus in the fourth race, a 100 to 1 shot, heavily played across the board, ran second."
