Fermented rice is what's left after the rice wine fermentation process. In a nut shell, during the rice wine making process, the yeast balls break the starches into sugar, then sugar into carbon dioxide and ethanol (or alcohol). Carbon dioxide would escape into the air, the liquid would be the rice wine and the sediment would be the fermented rice.
I'll write about the rice wine in another blog. Here, we don't want the fermented rice goes to waste. For that, it's common for Chinese people to cook egg drop soup, poached egg soup, or rice ball soup with the fermented rice.