Ganache is French. It is a liquid chocolate that people pour over candies and fudge. Sometimes, they will pour it on cakes or pies. It is considered to be a glaze or icing. Cream is used and is warmed on a stove. Different types of chocolate is used in ganache. It just depends on what is being made. For basic ganache, semi-sweet milk chocolate is used.
However, dark chocolate may be used too. When making ganache with panache, a white chocolate may be used. However, there may need to have more cream in the recipe when white chocolate is used. When glazing or icing a cake, a dark chocolate may be used in the recipe to make the ganache. It could also be used for a pastry.