Historically, the term "kodachi" was used more generically to refer to any sword that was shorter than a standard katana. It encompassed a range of shorter swords, including wakizashi (a short sword), tanto (a dagger or knife), or even a shortened katana. Therefore, the "kodachi" does not have specific defining characteristics but rather refers to the size or length of the sword.

In modern times, the term "kodachi" is sometimes used to describe a sword that is shorter than a katana but longer than a tanto. These swords often have a blade length between 50 to 65 centimeters (20 to 26 inches). However, it's important to note that this usage is more of a modern convention rather than a historical classification.

To summarize, the term "kodachi" is not a specific sword type in traditional Japanese weaponry, but rather a descriptor for a sword that is shorter than a katana.