During

We use during before nouns and noun phrases to refer to when something happens over a period of time. During can refer to the whole time of the event:

You are not allowed to use your mobile phone during class. (the whole of the class)

I have to have my window open during the night. (the whole of the night)

In this meaning, during can often mean the same as in:

His grandfather fought in the army during the First World War. (or … inthe First World War.)

When I was a kid, our cousins often came to stay with us during the summer. (or … inthe summer.)

During can refer to something that happened while the main event was taking place. In such contexts, during means ‘at some unspecified point in time’ and is more common than in:

What was that noise I heard during the night, I wonder? or … in the night. (I heard a noise at an unspecified point in the night.)

One day, during the Second World War, her father just disappeared. (He disappeared at an unspecified point.)

Warning:

We don’t use during when we refer to numbers and lengths of time. In this case, we use for:

They lived in Edinburgh for four years.

Not: They lived in Edinburgh during four years.

However, we can use during with the first or thelast + length of time or time expression:

During the first three years of the war, 50,000 civilians were killed. (during refers to when this happened.)

I haven’t done any exercise during the last week. (during refers to when I didn’t do exercise.)