For shows how long something happened. It is used to refer to a period of time. For example:
- We're ging to live in Malta for 6 months.
- She's in New York for a few days.
- We went to Saudi Arabia for a week.

See also the related unit on the Present Perfect and since.

Both during and while refer to a period of time in which something happens. For example:
- My phone rang while I was in a meeting.
- My phone rang during the meeting.

During is used with a noun or noun phrase. For example:
- We were busy during the weekend.
- During the night the cat woke me up.
- The Athenians suffered heavy losses during the battle of Salamis.

While is used with a subject and verb. For example:
- We went shopping while you were sleeping.
- You shouldn't eat while you are in the library.
- While I was working I got an email from Tamara.

When and while can both be used when two things happen at the same time.

When two continuous actions happen at the same time, we usually use while. For example:
- "While you were studying I went out shopping." Studying and shopping are actions.

When two short events happen at the same time, we use when. For example:
- "When I saw you I didn't recognize you." I saw you and I didn't recognize you are individual events.
- I heard you when you opened the door.
In this situation while is incorrect. For example:
"While I saw you I didn't recognize you."

When one continuous background situation occurs and one shorter event occurs at the same time, when and while can both be used. For example:
- "When I was in Rome I met my wife." - "While I was in Rome I met my wife."
- "I cut myself while I was cooking dinner." - "I cut myself when I was cooking dinner."

The position of while and when clauses is interchangeable with usually little difference in meaning.
- Don't forget to lock the door when you go out. - When you go out don't forget to lock the door.
- We're still growing while other businesses are losing clients. - While other businesses are losing clients, we're still growing.

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