A full tang katana refers to a type of katana sword in which the tang extends the entire length of the handle. The tang is the part of the blade that extends from the blade's base into the handle, connecting the blade to the hilt.

In a full tang katana, the tang is a solid, continuous piece of metal that runs the entire length of the handle, providing strength, stability, and durability to the sword. The handle scales or tsuka are typically attached to the tang, providing a grip for the wielder.

A full tang construction is considered desirable in a katana because it ensures that the blade and handle are securely connected, minimizing the risk of the sword breaking or becoming loose during use. It also contributes to the overall balance and strength of the sword.

A full tang katana is achieved through the traditional construction method known as "through-tang" or "nagamaki." This construction style involves inserting the tang into the handle and securing it with a wooden peg called a mekugi, which is driven through corresponding holes in the tang and handle.

Having a full tang construction is considered a mark of quality and authenticity in katana swords. It is a feature often sought after by practitioners of martial arts, collectors, and enthusiasts who appreciate the traditional craftsmanship and reliability of a well-constructed katana.