Investopedia上将Tax loss carryback, carryforward定义为：

A tax benefit that allows business losses to be used to reduce tax liability in previous and or following years.  

请问：①这里的tax benefit是DTA吗？②如果是DTA可以reduce tax L. in following year是无疑的，但怎么能减少tax in previous years呢？麻烦举例。谢谢各位大牛牛指导～！