* Quand - This is the most common translation for "when" as a question word, asking about time. For example: "Quand vas-tu partir?" (When are you going to leave?)
* Lorsque - This is used for "when" as a conjunction, indicating time or circumstance. For example: "Lorsque j'ai vu mon ami, j'étais très heureux." (When I saw my friend, I was very happy.)
* Dès que - This means "as soon as" or "when" in the sense of something happening immediately after another event. For example: "Dès que tu arrives, appelle-moi." (As soon as you arrive, call me.)
* Au moment où - This is a more formal way of saying "when" and is used for specific moments in time. For example: "Au moment où la sonnerie a retenti, j'étais en train de lire." (When the bell rang, I was reading.)
To provide the most accurate translation, please provide the full sentence or context in which you want to use "when."