What is a 2.9 Board foot?

A board foot is 12 inches by 12 inches, 1 inch thick. Any combination of measurements that equal this is 1 board. 6x24x1 is 1 board foot. 2.9 board foot could be anything. There should be another measurement saying what this is. Board foot is used to figure cost as most common wood is the same price per board foot. Could be 2x4, 2x12 or 1 inch, it all works out the roughly the same price.