Arpeggio means "broken chord." The note of a chord played in rapid succession, but no more than one note at a time, is an arpeggio. For example, a C major chord contains the notes C, E, G, and another C in a different octave. So playing "C-E-G-C(an octave up from first C)-G-E-C" would be an arpeggio, because the notes are in the chord, and are only played one at a time.