Most of you will know that this is 'goodbye' in French (more literally, it means something like 'until we see each other again', voir being the verb 'to see').
Many people contract au revoir when speaking to something that sounds more like 'oh-vwar', but it is not unusual in the Touraine to hear someone give it the full Edith Piaf treatment – 'oh rrrrrrrevwwaarrrrrrrah'. Curiously, this method of delivery is particularly common amongst female motorway toll booth cashiers. That's right, you do not just hand over your toll (which can be anything from 90c to €26.50, depending on where you are). You greet one another with bonjour, you say violà when you hand over the money, the cashier says merci, then when you are handed your receipt you salute one another again with a chorus of merci, bonne journée, au revoir. The same routine is performed with supermarket cashiers and indeed any shopping transaction. It is important to bid your fellow shoppers bonjour and au revoir in a general salute as you enter and leave the shop too, whether you know them or not.
In other situations there are other ways of saying goodbye:
- à toute à l'heure – this is used if you have arranged to see the other person at some specific time, usually later the same day, or at most at some time in the next few days. I learnt this one at school, but then forgot about it until one day I made a booking at Auberge St Nicolas for dinner later the same day and the nice woman who runs the place sent me on my way with à toute à l'heure.
- à bientôt – 'see you soon' – for the casual friendly social situation or encounter in the street or market with neighbours.
- à la prochaine – 'until the next time' – useful for when leaving the bar.
- à demain – 'until tomorrow', 'see you tomorrow'.
- adieu – I have never actually heard anyone use this. I am guessing it is considered very old-fashioned, especially as it means 'with God' – probably Napoleon outlawed it or something.