A katana (刀 or かたな) is a Japanese sword characterized by a curved, single-edged blade with a circular or squared guard and long grip to accommodate two hands. Following tachi, it was used by samurai in feudal Japan and worn with the blade facing upward. Also, since the Muromachi period, many old tachi were cut from the root and shortened, and the blade at the root was crushed and converted into katana. The official term for katana in Japan is uchigatana (打刀) and the term katana (刀) often refers to single-edged swords from around the world.

The katana belongs to the nihontō family of swords, and is distinguished by a blade length (nagasa) of more than 2 shaku, approximately 60 cm (24 in).

Katana can also be known as dai or daitō among Western sword enthusiasts, although daitō is a generic name for any Japanese long sword, literally meaning "big sword".

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