A faux pas (French: false step; pronounced foh-PAH) is a violation of accepted, although unwritten, social rules.
Faux pas are very culture specific; what is considered good manners in one culture can be considered a horrible faux pas in another. For example, in America it is usually considered good manners to bring a bottle of wine when coming to someone's house for dinner. In France, however, this is considered insulting as it implies that the dinner-hosts are unable to provide their own good wine.
See also: most common Wikipedia faux pas\n