Across The Board

The board used to be the chalkboard where actual stock prices were written down in the 19th century with actual chalk. Like...the dust kind that gives you lung cancer. The New York Stock Exchange was the big board. It was about the size of a paddle tennis court, and they would write in large letters across it. There were days when the entire market went up and the scribe charged with writing the stock prices down would then add a plus sign or adjust the numbers...across the board.

Across the board simply means that, in an entire subset of events, the same thing is generally happening. Like, on a given day, all tech stocks went down, or the weather was raining across the board in every city in the U.S. Except in Phoenix, of course.