Tremolo

Tremolo, or tremolando, is a musical term that describes various trembling effects, falling roughly into two types. The first is a rapid reiteration

• of a single note, particularly used on bowed string instruments and plucked strings such as harp, where it is called bisbigliando or "whispering".
• 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 (somewhat misnamed) device called a "tremolo arm" or "whammy bar" that allows a performer to lower or raise the pitch of a note or chord, which is known as vibrato. This non-standard use of the term "tremolo" refers to pitch rather than amplitude.