During有两个意思：
1.from the beginning to the end of a period of time 这时不可以用in替代.
2.at some point in a period of time可以用in替代.
My father was killed during the war.
I mentioned the subject during our discussions at her Washington office.
比较：
I met him sometime during the week.（反复,不能用in代替） 我是在这一周的某天遇到他的.
during the holiday 强调假期的从头到尾
He enjoyed himself during his holiday.
in the holiday 强调这段时间其中某一点时间,并不表示自始至终