La plume de ma tante (phrase)

La plume de ma tante ("the quill of my aunt") is a phrase attributed to elementary French language instruction (possibly as early as the 19th century) and used as an example of grammatically correct phrases with limited practical application that are sometimes taught in introductory foreign language texts. As Life magazine said in 1958, "As every student knows, the most idiotically useless phrase in a beginner's French textbook is la plume de ma tante (the quill of my aunt)." The phrase is also used to refer to something deemed completely irrelevant.

Source: Wikipedia — La plume de ma tante (phrase) (CC BY-SA 4.0)