In music, tremolo (Italian pronunciation: [ˈtrɛːmolo]), or tremolando ([tremoˈlando]), is a trembling effect. There are two types of tremolo.

The first is a rapid reiteration:

• Of a single note, particularly used on bowed string instruments, by rapidly moving the bow back and forth; plucked strings such as on a harp, where it is called bisbigliando (Italian pronunciation: [bizbiʎˈʎando]) or "whispering". Tremolo picking, on traditionally plucked string instruments including guitar and mandolin, is the rapid articulation of single notes or a group of notes with a plectrum (pick) or with fingers. Tremolo playing sustains notes that would otherwise rapidly decay (fade to silence).
• Between two notes or chords in alternation, an imitation (not to be confused with a trill) of the preceding that is more common on keyboard instruments. Mallet instruments such as the marimba are capable of either method.
• A roll on any percussion instrument, whether tuned or untuned.

A second type of tremolo is a variation in amplitude:

• As produced on organs by tremulants
• Using electronic effects in guitar amplifiers and effects pedals which rapidly turn the volume of a signal up and down, creating a "shuddering" effect
• An imitation of the same by strings in which pulsations are taken in the same bow direction
• A vocal technique involving a wide or slow vibrato, not to be confused with the trillo or "Monteverdi trill"

Some electric guitars use a (misnamed) lever called a "tremolo arm" or "whammy bar" that allows a performer to lower or (usually, to some extent) raise the pitch of a note or chord, an effect properly termed vibrato or "pitch bend". This non-standard use of the term "tremolo" refers to pitch rather than amplitude. However, the term "trem" or "tremolo" is still used to refer to a bridge system built for a whammy bar, or the bar itself. True tremolo for an electric guitar, electronic organ, or any electronic signal would normally be produced by a simple amplitude modulation electronic circuit. Electronic tremolo effects were available on many early guitar amplifiers. Tremolo effects pedals are also widely used to achieve this effect.