Cooking Sake (ryorishu) is used to give a delicious rich flavour to your fish and meat dishes, or to soften strong flavoured ingredients. It is most famously used to make sweet sauces such as teriyaki and yakitori, or to soften strong flavoured ingredients.
Manufacturers are required by law to add salt (2-3%) to cooking wine to make it unfit for drinking, so that shops without alcohol license can carry the products.
Similar to cooking sake is Mirin a sweet rice wine which has a lower alcohol content but higher in sugar content.