A katana without a guard is commonly referred to as a "guardless katana" or "tsuba-less katana." The term "tsuba" specifically denotes the handguard on a Japanese sword, including the katana. The primary function of the tsuba is to protect the wielder's hand and to provide stability during sword techniques.

However, in certain cases, a katana may be intentionally crafted or displayed without a tsuba for various reasons. This can be seen in specific martial arts training or practices where the absence of a guard allows for a lighter weight, improved maneuverability, or a different gripping experience. In these cases, the sword is often referred to as a guardless katana or a tsuba-less katana.

It's important to note that a katana without a guard should still possess other integral components such as the habaki (a metal collar that secures the blade in the scabbard), seppa (spacer washers), and a properly wrapped tsuka (handle) with tsuka-ito (handle wrapping).

While a tsuba-less katana may have its practical or stylistic applications, it's worth mentioning that the tsuba serves an important purpose in traditional katana design by providing protection and balance. Most katana swords are typically equipped with a tsuba for optimal functionality and to uphold the traditional aesthetic.