DIN stands for Deutsches Institut für Normung, the German Institute for Standardization. It was originally known as "Normenausschuss der Deutschen Industrie (NADI)", the Standards Association of German Industry. The institute was founded in 1917 and became part of the ISO, International Organization for Standardization, in 1951. The organization takes part in the international work of standardization and sets up the technical standards in Germany (the DIN standards). Some standards have been accepted worldwide, for example the dimensions of several cable connector types like those used between MIDI devices (specification DIN 41524).
Sources of information:
http://www.din.de/