Kitchen knives in the context of "Takefu"

A knife (pl.: knives; from Old Norse knifr 'knife, dirk') is a tool or weapon with a cutting edge or blade, usually attached to a handle or hilt. One of the earliest tools used by humanity, knives appeared at least 2.5 million years ago, as evidenced by the Oldowan tools. Originally made of wood, bone, and stone (such as flint and obsidian), over the centuries, in step with improvements in both metallurgy and manufacturing, knife blades have been made from copper, bronze, iron, steel, ceramic, and titanium. Most modern knives have fixed or folding blades, with styles varying by maker and country.

Knives can serve various purposes. Hunters use a hunting knife, soldiers use the combat knife, scouts, campers, and hikers carry a pocketknife; there are kitchen knives for preparing foods (the chef's knife, the paring knife, bread knife, cleaver), table knife (butter knives and steak knives), weapons (daggers or switchblades), knives for throwing or juggling, and knives for religious ceremony or display (the kirpan).

Sharpness refers to the ability of a blade, point, or cutting implement to cut through materials with minimal force, and can more specifically be defined as the capacity of a surface to initiate the cut. Sharpness depends on factors such as the edge angle, edge width, and the fineness of the cutting edge, and is aided by material hardness. This quality is found in a variety of naturally occurring forms, including certain kinds of rock, in plant thorns and spines, and in animal teeth, claws, horns, and other structures serving various purposes. Sharpness is also a critical attribute for man-made tools ranging from kitchen knives and scissors to industrial cutting equipment, as it allows the user of a sharp implement to efficiently penetrate surfaces, or neatly divide other materials into smaller portions as needed.

A balance must be found between the sharpness and durability. Methods that can circumvent this include differential hardening. This method yields an edge that can hold its sharpness as well as a body that is tough. Different methods have been developed to sharpen surfaces, and to test surfaces for relative sharpness.