我记得老师过去说过，during 后面的名词一直要用定冠词的（当然也可用物主代词等）：
It rained a fair bit during the night. 夜间下了不少雨。
She was punished for copying during the examination. 她因考试作弊而遭到处罚。
I took a lot of photos during my holiday. 我在度假期间拍了很多照片。
Please act for me during my absence. 我不在时请代理我处置事务。
We have no real conception of what people suffered during the war. 大家没办法确切知道战时大家的苦难。
但下面这句为何没用定冠词呢？
Students must remain in residence during term. 学生于学期中需要住校。
▲这个问题跟介词 during 没关系，重要是 term 的词义和使用方法。当 term 表示学校的学期时，假如不是特指，通常可以不需要冠词。比如：
the last day of term 学期最后一天（《柯林斯词典》）
The train also makes the run back again to London at the end of term in June. 这趟列车也在6月学年结束时返回伦敦。
At the end of term we held a class party and we all had to cook something. 学期末，大家班开了一个派对，大家每一个人都要为派对做点吃的。
所以说，你这个句子并很好：
Students must remain in residence during term. 学生于学期中需要住校。
▲假如需要特指某个学期，则要加定冠词或指示代词。比如：
Are there any exams at the end of this term? 这个学期期末有考试吗？
He had no trouble with discipline that term. 那学期在他的课上，没不守纪律的。
You’re just going to sell them at the end of the term. 你也要计划在这个学期末把它们卖掉。
除此之外，与学校有关的一些词汇，如school，class，compus，总是不需要冠词，如：
after school
before school
after class
at the end of class
during class
on compus
