In music, an arpeggio is a broken chord where the notes are played or sung in sequence, one after the other, rather than ringing out simultaneously. The word, like many other musical terms, originates from Italian, in which it means "in the manner of the harp."
An arpeggio is a group of notes which are played one after the other, either going up or going down. The notes all belong to one chord. The chord may, for example, be a simple chord with the 1st, 3rd and 5th notes of the scale in it (this is called a "tonic chord"). An arpeggio in the key of C major going up two octaves would be the notes (C,E,G,C,E,G,C).
An arpeggio is a type of broken chord. Other types of broken chords play chord notes out of sequence or more than one note but less than the full chord simultaneously. Arpeggios can rise or fall for more than one octave.
An "arpeggiated chord" means a chord which is "spread", i.e. the notes are not played exactly at the same time but are spread out. Harps very often play arpeggiated chords. In piano music they are quite often used. An arpeggiated chord is written with a wiggly line going from top to bottom in front of the chord. An arpeggiated chord is spread from the lowest to the highest note. Occasionally composers such as Béla Bartók ask for them to be played from top to bottom. This is shown by adding an arrow pointing down. Arpeggio's are known at the end of scales.
In Western classical music, a chord that is played first with the lowest note and then with successive higher notes joining in is called arpeggiato. Sometimes this effect is reversed, with the highest note coming first. In some modern popular music arpeggiato is called a "rolled chord".
In early computer music, arpeggios were often the only way to play a chord since sound hardware usually had a very limited number of oscillators. Instead of tying them all up to play one chord, one channel could be used to play an arpeggio, leaving the rest for drums, bass, or sound effects.