Basically an extension of the word "fuck" but with a little more edge and conviction. Back then, it did have something to do with an individuals mother but today, people use it loosely i.e. movie dialogue, music, art/graffiti and it has nothing to do with anybodies mother. It may have started as an expression in most African-American communities but it has become one of the most universal words on earth.
Song: "There he go (x3) (GET DAT MOTHERFUCKER!)" -Mystikal (There He Go)
Movie: "You're rent's due motherfucker!" -Samuel L. Jackson
Person on the street: "Hey you bitch ass motherfucker, I got you!"