1) The root of a chord.
2) The lowest note found in the harmonic series.
Overtones
The notes that are found in a harmonic series excluding the fundamental notes.
Harmonic Series
A series of notes (otherwise known as overtones) that vibrate above a note.
Harmonics
1) A note that is in the harmonic series. These notes are exceptionally clear and pure.
2) A high pitched musical note that is played by amplifying particular overtones over the fret on a guitar string.