Vinegars are widely used in Asian cooking. Unlike Western kinds, they are usually made from rice. There are many varieties, ranging in flavour from the spicy and slightly tart to the sweet and pungent.
Two kinds of rice vinegar are used in these recipes: white and black. Both can be found in Asian grocers and supermarkets. They are sold in bottles and will keep indefinitely.
If you cannot get them, you can substitute cider vinegar. Malt vinegar can be used, but it is stronger and more acidic. Never simply substitute Western white vinegar for rice vinegar: the contrast is too great.