The most common way to say goodbye in French is "Au revoir" (pronounced "oh-re-vwahr").
Here are some other ways to say goodbye in French, depending on the context:
* "Ciao" (informal, borrowed from Italian)
* "Salut" (informal, can also mean "hello")
* "Bonne journée" (literally "good day," used in the afternoon)
* "Bonne soirée" (literally "good evening," used in the evening)
* "Bonne nuit" (literally "good night")
Perhaps you're thinking of a specific French expression that you heard? If you can give me more context, I might be able to help you understand what you're looking for.