A traditional katana has a slight curve along its blade. This curve is often referred to as the "sori" in Japanese. The sori contributes to the functionality and aesthetics of the katana.

The curve of a katana blade typically begins near the base (near the hilt) and gradually increases towards the tip. The amount of curve can vary between different katana swords, but in general, the curve is relatively gentle and subtle.

The purpose of the curve in a katana is multifaceted. It allows for more effective and efficient cutting techniques by facilitating a slicing motion. The curve enables the sword to maintain contact with the target for a longer duration during a cut, enhancing the cutting performance.

Additionally, the curve also assists in fluid drawing and sheathing of the katana from the saya (scabbard). The curvature allows for a smoother and quicker motion during the drawing process, enabling the samurai to draw and strike in a single fluid motion.

It's worth noting that the specific degree and measurement of the curve, as well as the other dimensions of the katana blade, can vary between individual swords and different swordsmiths. The curvature is carefully considered and crafted to achieve a balance of functionality, aesthetics, and overall performance.

In summary, a traditional katana features a slight curve along its blade, known as the sori. This curve contributes to the sword's cutting efficiency, drawing and sheathing techniques, and overall aesthetics. While the degree of curve can vary, it is generally a gentle and subtle curve that enhances the katana's functionality and distinctive appearance.