Arpeggios are, essentially, chords that are broken out into single note patterns. For example, instead of playing a four note C Major 7 (C, E, G, B) chord where you strum all the notes at once, a C Major 7 arpeggio would have you play C, E, G, B as single notes in a four note pattern. Arpeggios are a great improvisation tool, and understanding arpeggios is vital to realizing how to construct solos that sound more emotive and unique. To that end, triad arpeggios also exist, are equally useful, and are constructed in the same way — they just have one less note.