The term "Dai katana" is not a widely recognized or commonly used term in traditional Japanese sword terminology. It is possible that it is a misspelling or a misinterpretation of "Daito" or "Daitō."

"Daito" is a term used to refer to a long sword or a large-sized katana. The word "daito" translates to "big sword" or "long sword" in English. It is the opposite of "shoto," which refers to a shorter sword or a wakizashi. The daito, being longer than a standard katana, typically has a blade length of around 70 to 90 centimeters (27 to 35 inches).

The daito, like other traditional Japanese swords, has a curved single-edged blade, a tsuka (handle), and other fittings like the tsuba (handguard) and saya (scabbard). It follows the same design principles and forging techniques as a regular katana.

However, it's important to note that the categorization of a sword as a "daito" may depend on the specific context or usage. In some cases, the term may be used to describe a particular style or variant of a katana, emphasizing its size or length.

In general, the term "daito" is less commonly used in everyday discussions about Japanese swords compared to more well-known terms like katana, wakizashi, or tanto. Instead, the specific measurements and categorization of a sword are typically described using blade lengths or the traditional classifications of katana, wakizashi, and tanto.