A Fender CD-140S dreadnought. Note the broad waist and wide lower bout. You see it all the time when shopping for an acoustic guitar—terms such as “dreadnought,” “concert,” “jumbo,” “parlor,” “auditorium,” etc. These names aren’t merely marketing-speak; they are long-established conventions for specific flat-top steel-string acoustic guitar body shapes and sizes (some of which date back more than a century...