Daisho means, in a manner of speaking, "long short". It refers to the twin swords
The "long" sword is the katana. It could be used one or two handed, and is single edged. Samurai treasured their katana, and many stayed within a family for generations. It was considered unlawful for any but a samurai to wield the katana.
The "short" sword is the wakizashi. It is one-handed and single-edged. While a wakizashi is built in much the same manner as a katana, and thus about as costly to make, it was not considered unlawful for those outside the ranks of the samurai to wield them.
The process by which the swords were forged was supposedly a closely kept secret. The stock was folded multiple times, and then reforged after each folding. The blade is curved and chisel-pointed, so that it could pierce lamellate armor, if need be. The construction process resulted in a blade that was strong, yet flexible.
The two swords were generally both worn on the samurai's left side, with the scabbards thrust into the sash, edge-side up.