Rice vinegar is pretty much exactly what it sounds like: vinegar made from fermented rice instead of the fermented grapes or apple cider that are common in western cooking. Rice vinegars have been used in East Asia for thousands of years and are instrumental both for cooking and pickling in many cuisines across the continent.
A significant difference between the tastes of rice vinegar versus more conventional western vinegars is the apparent lesser acidity of rice vinegar; while western vinegars are almost unbearably tangy at times, rice vinegars are typically smoother and less overpowering. Depending on the type, rice vinegars come in a variety of colors from clear to dark black, light yellow or even red.
Rice vinegar is a ubiquitous ingredient in Japanese, Chinese, and Korean cooking and can also be found in many Southeast Asian dishes. It is often used in sauces and perhaps most popular as a key ingredient in making sushi rice.