Skullcandy FMJ and Skullcandy FMJ 09 refer to earphones. “FMJ” stands for “Full Metal Jacket.” Skullcandy FMJ 09 refers to a particular model of FMJ ear buds. Skullcandy separates the earphones into two categories; buds and in-ears. Buds are the earphones which sit and get adjusted inside the ear.