"The cord is a unit of measure of dry volume used to measure firewood and pulpwood. A cord is the amount of wood that, when 'ranked and well stowed' (arranged so pieces are aligned, parallel, touching and compact), occupies a volume of 128 cubic feet." (From our good friends at
Wikipedia.)
In case you didn't get that the first time around, how about a visual?
This picture is the woodpile at the Husker Barn here on Arington Tree Farm. The red diagram shows the dimensions of a full cord of wood, or 128 cubic feet (click the photo to enlarge it). Let's do some math!