To take French leave means to leave a party or other gathering without saying goodbye to the host. In social situations, this often occurs when a person must leave at a time when it would be rude or inconvenient to take leave loudly. There is also a military usage of the phrase, in which it is applied to people who have gone absent without leave (AWOL). Whether taking French leave is acceptable in social situations is a point of much contention and deciding whether to say a formal goodbye to the host at a party is often a difficult social navigation.
The origin of this phrase is not firmly identified, but it may have its roots in military interactions. Some attribute the phrase to Napoleonic encounters, while others associate it with American engagements. It is also possible that it arose out of French traditions that were foreign to English speakers.
At large parties, it is often considered socially acceptable to take French leave if the host is unavailable for a quick goodbye. When attending small parties, this action would almost always be considered socially unacceptable. In large gatherings, however, it is often more of an inconvenience to the host for each guest to receive an elaborate farewell. Usually, it is recommended that a person taking French leave call the next morning to thank the host or have a friend at the party notify the host of his or her departure with appropriate gratitude. Some etiquette specialists feel that this type of exit is inappropriate in all situations because it may offend the host.
In some contexts, to take French leave can mean to do something without permission, particularly when it involves an absence. For example, a person might be said to take French leave when skipping class or work. This use is almost always meant to imply that the absence was inappropriate, which is quite different from the use applied to social situations.
Some people worry that using this term might be considered anti-French, but it is interesting to note that both the French and Italian languages attribute this same action to the English. Given the relatively innocuous and often considerate nature of the act, it is usually not considered offensive to use the term. It is also important to remember that in some cultures taking French leave may be considered highly inappropriate no matter the situation, and it is always better to be cautious when dealing with unfamiliar customs.