Sake is a traditional Japanese alcohol. Although it is sometimes called rice wine, sake is produced by a brewing process more similar to beer than wine. Sake adds a delicate sweetness, fragrance and depth of flavour to dishes.
There are cooking sakes available, but I would recommend using a cheaper drinking sake for cooking, similar to how you might use a red or white wine in Western cooking. Similarly, cooking concentrates the flavour so starting with a sake that you would like to drink is preferable.