A Katana is a Japanese sword derived from the uchigatana. It is primarily a long slashing weapon with a single cutting edge. The handle may be bound with a fabric strip and rayskin or leather instead of wire but these wrappings differ with personal preference and time frame. Often (but not always) a katana is hilted with a disc called a tsuba; these can vary from extremely plain to highly artistic.
The blade is made by a swordsmith using the folding method, in an attempt to remove the impurities present in the poor quality raw materials available to Japanese smiths. However, they were not folded hundreds of times, as popular myth has it. After being folded about 20 times, folding ceases to add at all to the sword's quality, and will actually cause the steel to lose too much carbon and become iron. Most commonly katana were folded 12 times (san mai).
Katana were produced in their thousands and at least 200,000 were made for export during the medieval period. Most modern people refer to the exceptional quality blades rather than the more common blades.
Debate rages as to whether katana are truly superior to European swords, as is often believed, or if it's more to do with situation or preference.
Katana are mundanely referred to as samurai swords. The ninja swords (ninja-to) of modern Hollywood myth are an adaptation of a late Edo period katana. However, there is no evidence that this type of sword was used prior to this time. Historical records indicate that the 'ninja' used the same weapons as other bushi.