Katanas are typically curved swords. The distinctive curved shape of the katana blade is one of its defining characteristics. The curve of the blade allows for efficient cutting and slicing motions, as well as providing balance and stability during use.

The curvature of a katana varies, but it generally follows a gentle curve along the length of the blade. The curve starts from the hilt and gradually increases towards the tip, creating a shape known as the "sori." The curvature enhances the cutting performance of the katana, as it helps to distribute the force of the cut along the edge and allows for a smoother motion when drawing the sword.

The curved design of the katana also offers advantages in terms of blade dynamics, balance, and maneuverability. It contributes to the katana's overall effectiveness as a cutting weapon, allowing for precise and powerful strikes.

It's worth noting that there are other types of Japanese swords, such as the tachi, which can have more pronounced curvature compared to the katana. Additionally, there are straight-bladed Japanese swords, like the chokuto, which predate the curved designs of the katana.

However, when referring to the traditional katana that is most commonly associated with the samurai, it is characterized by its gentle curve along the blade.