“This policy applies across the board”.
Across the board is a common phrase, it means “generally applicable” or “the general rule” which is not a surprise, you can deduce it from the original words.
When I read it in a memo recently I was triggered to question the origins. I had assumed that it came from Chess or some similar board game. In fact it comes from racing, where in US parlance an “across the board” bet is one where equal amounts are placed on the same contestant to win, place, or show.
Surprisingly it’s not that old – apparently first recorded about a hundred years ago, in a report of a race in Atlanta.