Stockfish is a preserved fish, while salting is one way to preserve fish, stockfish is a dried fish. Norway is historically known for it's stockfish, in Northern Norway, wooden outdoor racks exposed to wind and sun is part of the scenery.
During the curing of the fish about eighty per cent of the moisture is removed from the fish, being that all nutrients are retained in the stockfish, making it a very healthy food.
Stockfish as you may easily inquire can be made from almost all species of fish, although the most common are cod, and other white fish like pollack, ling, haddock and tusk. 
After being captured the fish is immediately prepared to stockfish. The fish can be dried whole or split, the fish can be dried outdoors or done in artificial dryers. The split fish is normally cut along the spine with tail. Drying outdoor is seasonal, it is done from February til May.
Why is stockfish and Norway so attached, well to start with Norway has one of the worlds best fishing fleets. Plus they have the fish close to shore. Then they also have weather that guarantees the whole drying procedure outdoors. The cold temperature is something quite common between February and May in Northern Norway, therefore it protects the fish that is hanging in the wind and sun from bacteria and insects. The temperature slightly above zero is great, as too cold will destroy the quality of the fish, the Lofoten area is known to be the best place for stockfish production outdoors as it has very stable climate conditions which are appropriate for stockfish drying. Also fishing season also coincides with the best drying conditions.
The drying of the stockfish is not all done outdoors, after hanging on the racks for about 3 months it is then is moved indoors to a dry and aired area, here it will mature for another 2 months.
The stockfish is sorted by specie, quality and size. In Norway stockfish is usually consumed as a snack and to do the Scandinavian
The consumption of stockfish is world-wide African countries buy as it's a well preserved seafood and easier to handle. Italy and Croatia are also good markets for such fish. In Norway you will have some consumption namely to do lutefisk a Nortic dish. In Italy it goes by stoccafisso.
Due to being a healthy food with very nutritious ingredients stockfish is also used in pet food, obviously using defect products or lower quality outputs from processing plants.
As mentioned, stockfish is a historical product, it has been one of the most traded product by Norwegian businessmen since 1400.