A ball marker is a small, flat object used in the game of golf to mark the position of a player's ball on the green. When a player needs to lift their ball to clean it or allow another player to putt, they place the ball marker on the ground to indicate where the ball was located. Ball markers can come in various shapes and materials, including metal, plastic, or even coins. Many golfers personalize their ball markers with unique designs or logos, making them a fun accessory while also serving a practical purpose on the course.