http://revision3.com/tzdaily/2007-12-26ferrite/
A ferrite bead is a passive electric component used to suppress high frequency noise in electronic circuits. Ferrite beads employ the mechanism of high dissipation of high frequency currents in a ferrite to build high frequency noise suppression devices. Ferrite beads may also be called ferrite cores, ferrite rings, ferrite EMI filters, or mistakenly as ferrous beads. Engineers often jokingly call them FCC goobers, or FCC lumps after their shape when attached to a cable. -
http://en.wikipedia.org/wiki/Ferrite_bead