A "Bo Hi" sword refers to a type of sword that features a groove or channel running along the blade. The groove is commonly known as a "Bo Hi" or "fuller." The Bo Hi is a distinctive characteristic of certain sword designs and serves both functional and aesthetic purposes.

Functionally, the Bo Hi serves to lighten the weight of the sword without compromising its structural integrity. By removing material from the blade through the groove, the overall weight of the sword is reduced, making it easier to wield and maneuver. The removal of material also shifts the center of gravity of the sword, potentially improving its balance and handling.

Aesthetically, the Bo Hi adds visual interest to the blade. It creates a decorative element that can be combined with other design elements, such as the hamon (temper line) or intricate engravings, to enhance the overall appearance of the sword. The Bo Hi can vary in width and depth, and its shape and placement on the blade can also contribute to the sword's visual appeal.

While the Bo Hi is commonly associated with Japanese swords like katanas, it can also be found in other sword traditions around the world. The presence of a Bo Hi on a sword is a matter of personal preference, and not all swords, even within the same style or type, will necessarily have a groove. Some sword enthusiasts appreciate the functional and aesthetic benefits of a Bo Hi, while others may prefer swords without it.

It's important to note that the Bo Hi is primarily a design feature and does not significantly affect the functionality or cutting performance of a sword. The blade's construction, materials, and overall craftsmanship are still the most critical factors determining a sword's quality and performance.