Harmonic timbre
A timbre is harmonic when its frequency spectrum has the property that all overtones are exact multiples of the lowest frequency (as is the case with most methods of sound production, including the human voice, most instruments, and square, saw, and triangle waves). This causes the sound wave to be periodic (where the frequency of the sound wave is the frequency of the lowest note in the spectrum) and causes just intervals to be concordant.
A timbre can be said to be nearly harmonic if its overtones are approximately equal to integer multiples of the fundamental frequency. The frequency spectra of pianos, harpsichords, and any string instrument with plucked strings such as the guitar, as well as the violin, viola, cello, and upright bass when played pizzicato are examples.
A timbre is inharmonic if its overtones deviate significantly from integer multiples of the fundamental. Examples include bells, gamelans, and drums.