Fuzz: A fuzz pedal or "fuzzbox" is a type of overdrive pedal that clips a sound-wave until it is nearly a squarewave, resulting in a heavily distorted or "fuzzy" sound. Fuzzboxes may contain frequency multiplier circuitry to achieve a harsh timbre by adding complex harmonics. The Rolling Stones' song "(I Can't Get No) Satisfaction", with the main riff played by Keith Richards with fuzz guitar, greatly popularized the use of fuzz effects. Fuzz bass (also called "bass overdrive") is a style of playing the electric bass that produces a buzzy, overdriven sound via a tube or transistor amp or by using a fuzz or overdrive pedal.
source: Wikipedia