Most common:
* Erreur: This is the most general and common way to say "mistake" in French. It can be used in many situations, such as "j'ai fait une erreur" (I made a mistake).
Other possibilities:
* Faute: This is a slightly more formal word for "mistake" and is often used in contexts like grammar or spelling errors.
* Bêtise: This word carries a connotation of foolishness or stupidity and is used when the mistake is considered silly or careless.
* Méprise: This word is used when there is a misunderstanding or a misidentification.
The choice of which word to use depends on the specific situation and the level of formality.