What is the difference between C and D visas?
A C visa is a visa for a short stay ("short stay visa"). With a C visa, the total length of your stay in the Schengen area cannot exceed 90 days during any period of 180 days. The rules for C visas are common to all Schengen countries.
A D visa is an entry visa or a visa for long stay ("long stay visas"). A number of Schengen countries issue D visas for stays of more than 90 days. Each individual Schengen country decides the requirements for granting a D visa. This type of D visa gives access to travel in other countries in the Schengen area than the country that issued the D visa for up to 90 days during any 180-days period.
Norway issues D-visas as entry visas, most often to those who have recently been granted a residence permit, or to those who have lost their residence card. This type of D visa allows you to travel in transit through other Schengen countries to Norway.