This refers to any of four different tree genera, but most often the genus Fraxinus (from the Latin term for “ash tree”). Specifically, two subspecies of Fraxinus americana are used for guitar bodies, most notably (but not limited to) Fender. There is the northern ash, which is very hard, heavy and dense, while the southern ash (most often called “swamp ash”) is a fairly lightweight wood. Many of the finest 1950s Fender guitars had swamp ash bodies that delivered just the right blend of brightness and warmth. It takes a finish quite well.