A phrase "cord of wood" or "cord of firewood" is probably a new one to you if you are new to the firewood dealing business or did not grow up around wood stoves. Yet, cord of wood is how firewood is being purchased and sold, certainly for and buy the end user.
In North America, cord of wood refers to a dry volume of well racked firewood logs (split or not) that measures to 128 cubic feet. It is important that logs are stacked in parallel so that volume of air between the pieces of wood is minimized. Very often, to properly measure the cord, one would arrange 4-ft long logs into a rectangular formation of 8 feet in length and 4 feet high.
According to Wikipedia, a cord of wood is also known as "standing cord," "kitchen cord," "running cord," "face cord," "fencing cord," "country cord," "long cord," and "rick."
Sometimes, verbal definitions may be confusing because they differ from formalized units of measurement. For example, a vast majority of fireplaces, wood stoves, or firewood ovens in North America are designed to burn pieces of wood of about 16 inches (41 cm) long or shorter, which is roughly 3 times shorter than an average length of a log from a standardized cord. Thus, an arrangement of firewood, which is 16 inch deep (the length of the long), 8 feet long and 4 feet high is often also referred to as cord. Some areas qualify such as "short" cord volume as the "face cord" or a "rik."
If you are a casual user of firewood in your fire pit, fire place or a wood stove, you may not use "cord" very often. However, knowing this concept is useful when purchasing firewood in small wholesale quantity (i.e. buy more than a $5-$7 4-5 logs wrapped in plastic for your camp fire). Assuming you do not have a preference for wood type or quality, at the very least, knowing the cord measure can help you compare "apples to apples" and make sure you don't overpay when shopping between different dealers.
Check out this image. Cord of wood, anyone?