During 是個介系詞，後接名詞或名詞片語，意為「在…期間」，而這是指某個事件、活動或時間從頭至尾的整個期間。例如：
- Don’t speak during the meal. (吃飯時別說話) － 整個吃飯期間
- You’re not allowed to talk during the exam. (考試時不可交談) － 整個考試期間
- Students are not allowed to use their cellphones during class. (學生不可在課堂上使用手機) － 整個上課期間
就此意思而言，during 通常與 in 同義。例如：
- During the summer season, all the hotels are full. (整個夏季所有旅館都客滿)
= In the summer season, all the hotels are full. - His grandfather was killed in action during the Second World War. (他祖父在第二次世界大戰期間陣亡)
= His grandfather was killed in action in the Second World War.
During 亦可指「在…期間的某個時候」。在這樣的上下文中，during 比 in 要來得常用。例如：
- I heard a loud noise during the night. (夜裡我聽見一聲巨響) － 在夜裡某個時候
- I woke up several times during the night. (夜裡我醒來好幾次) －在夜裡幾個不同的時候
- John was robbed during the journey. (約翰在旅行途中遭到搶劫) － 在旅行中的某個時候
－ 在這三個句子中，during 亦可用 in 來替代，但 in 不若 during 來得常用。
During 不可用來表示持續的時間或時間長度。這要使用 for。例如：
- Roy was out of the office for three days last week. (羅伊上週有三天沒來上班) (正)
Roy was out of the office during three days last week. (誤) - I haven’t played basketball for years. (我已經有好幾年沒打籃球了) (正)
I haven’t played basketball during years. (誤) - Emily has lived in Taichung for ten years. (艾茉莉已在台中住了十年) (正)
Emily has lived in Taichung during ten years. (誤)
雖然 during 與 while 都意為「在…期間」，但 during 是介系詞，而 while 是連接詞。所以，during 後面不可接子句。例如：
- Tony came while we were having (our) dinner. (我們正在吃晚餐時東尼來了) (正)
Tony came during we were having (our) dinner. (誤) - Mary didn’t drink at all while she was pregnant. (瑪麗懷孕期間滴酒不沾) (正)
Mary didn’t drink at all during she was pregnant. (誤) - I’ll take care of your pets while you are away. (你不在時我會照顧你的寵物) (正)
I’ll take care of your pets during you are away. (誤) - While (I was) in Taipei I visited a friend in hospital. (在台北時我去探望一位住院的朋友) (正)
During (I was) in Taipei I visited a friend in hospital. (誤)