Let's start with some examples of easy arpeggios to get a better idea of what one is. The current shredding movement has made the use of arpeggios seem a daunting task. What with full 6 and 7 note arpeggios played with a single sweep at blazing speed. But we needn't think of arpeggios in these terms. Arpeggios can be played slowly and deliberately to make a wonderful statement and outline the underlying chords.
Arpeggios can also be just a few notes.
A simple triad arpeggiated during a solo can be most effective and can really help soloists get away from the diatonic or pentatonic scale runs. Now both these examples are totally useful. The second example uses an arpeggiated A minor chord with a few variations. It is played more slowly so that the sound of the underlying A minor chord may be heard, and therefore complimented. So an arpeggio will just be selected notes from a scale too.