Motherfucker, sometimes abbreviated as mofo, mf, or mf'er, is an English-language vulgarism. It is a form of the profanity fuck. The word is usually considered highly offensive. In common usage, however, it is rarely used to refer to one person having intercourse with a woman who is a mother. Rather, the word usually refers to a mean, despicable, or vicious person; or any particularly difficult or frustrating situation. Conversely, it can be used positively, as a term of admiration, as in the term badass motherfucker (BAMF), meaning a fearless and confident person.

Fuck is an English-language profanity which often refers to the act of sexual intercourse, but is also commonly used as an intensifier or to convey disdain. While its origin is obscure, it is usually considered to be first attested to around 1475. In modern usage, the term fuck and its derivatives are used as a noun, a verb, an adjective, an interjection or an adverb. There are many common phrases that employ the word as well as compounds that incorporate it, such as motherfucker, fuckwit, fuckwad, fuckup, fucknut, fuckhead, fuckface, fucktard, and fuck off.