Similar in concept to a harmonic. Overtones are tones produced by an instrument (or sound source) that are higher in frequency than the fundamental. They may or may not coincide with the frequencies of a harmonic series (harmonics), but they usually do. The difference is that harmonics are always musically related to the fundamental in that they are integer multiples of it. Overtones of a sound are often exactly the same as its harmonics except the first overtone is considered the second harmonic because the first harmonic is the fundamental. Overtones are also sometimes called partials (more on them later).