What is the origin of the idiom "above board" and when to use it?

The origin of the idiom "above board" may have derived from the game of cards, specifically from the practice of placing one's cards openly on the table (above the board) to show that they were not concealed or manipulated. This act of transparency and fair play became associated with honesty and integrity. It is commonly employed in business, financial, and legal settings to describe transactions, negotiations, or practices that are conducted openly and in accordance with legal and ethical standards.