A folded steel katana refers to a type of katana sword that has undergone a traditional forging process involving the folding of the steel. The folding process is a technique used by Japanese swordsmiths to refine the steel, remove impurities, and create distinct grain patterns in the blade.

In the folding process, the swordsmith takes layers of steel and repeatedly heats, hammers, and folds them together. This process helps to homogenize the steel, distribute carbon evenly, and improve the overall quality of the blade. The layers are often stacked and folded multiple times, typically between 8 to 16 folds, although exceptional blades may have more folds.

The folding process in a folded steel katana creates a layered or "hada" pattern visible on the surface of the blade. This pattern is highly prized for its aesthetic appeal and is often a distinguishing characteristic of traditional Japanese swords.

It's important to note that the folding process alone does not determine the quality or performance of a katana. Other factors such as the choice of steel, heat treatment, blade geometry, and overall craftsmanship also contribute significantly to the final quality and performance of the sword.

Folded steel katanas are often sought after by collectors and enthusiasts due to their historical significance and traditional craftsmanship. However, it's worth noting that modern manufacturing techniques can produce high-quality katanas without the need for extensive folding, and the folding process itself may have limited impact on the performance of the blade in modern contexts.