Sound file: week-end
Qu’est-ce qu’il fait ce week-end ? – What’s he doing this weekend?
Week-end is a franglais word. I’ve always suspected that part of the reason it had to be imported into French from English was that the concept did not even exist for a long time: in France, the weekend is not always as free and clear for students and many employees as it is in other countries. French stores and banks are usually open on Saturday and, until 2008, so were schools (a change which has been debated ever since). When there was just one free day (Sunday) for students and many workers, the idea of the weekend—which really means “weekend off”—was far less important.
On the other hand, the French often turn one-day holidays into four-day weekends, when they font le pont.
The official French equivalent is la fin de semaine, though if you hear this in France, it’s more likely to mean "the end of the workweek" (Thursday / Friday) than "the weekend" (Saturday / Sunday). Even in formal contexts, the French are more likely to say le week-end if they’re referring to Satuday and Sunday.
In Québec, la fin de semaine meaning "the weekend" is much more common, though week-end may be used as well.