imperfect tense

基本解释

Instead of considering the imperfect tense as a specific tense, consider it as a time reference.
我们最好不要将未完成式视为一具体时式，而是视之为一参考性质的时间座标。
bccadets.org
If you are talking about something that is completely in the past, you use the Past Tense (sometimes called the Imperfect), e.g.
如果所谈论的事情完全发生在过去，则用过去时态(有时也叫做未完成时态)，例如：I used to live in Seattle /我过去住在西雅图。
edu.sina.com.cn
One thing you need to remember about the imperfect past tense—it is for activities that were ongoing or repeated; something you were doing in the past, or something you used to do.
你应该记住过去未完成式是指过去进行的或重复的动作，你在过去正在做的事或习惯的事。
blog.sina.com.cn