Harmonics and overtones are terms used to describe the different frequencies that are present in a sound wave. Here is a summary of what harmonics and overtones are based on the search results:

• Harmonics: A harmonic is a sinusoidal wave with a frequency that is a positive integer multiple of the fundamental frequency of a periodic signal. The fundamental frequency is also called the 1st harmonic, and the other harmonics are known as higher harmonics. Harmonics may also be called "overtones", "partials" or "upper partials". The difference between "harmonic" and "overtone" is that the term "harmonic" includes all of the notes in a series, including the fundamental frequency (e.g., the open string of a guitar). The term "overtone" only includes the pitches above the fundamental. In some music contexts, the terms "harmonic", "overtone" and "partial" are used fairly interchangeably.

• Overtones: An overtone is any partial higher than the lowest partial in a compound tone. The relative strengths and frequency relationships of the component partials determine the timbre of an instrument. The first permitted frequency over the fundamental is termed the first overtone, the next higher frequency is called the second overtone, and so on. The list of successive overtones for an object is called the overtone series. The first overtone as well as all subsequent overtones in the series may or may not be an integer multiple of the fundamental. Sometimes the relationship is that simple, and other times it is more complex, depending on the properties and context of the sound wave. Tones that cannot be multiplied or divided by a whole number are known as inharmonic overtones, or partial tones. When you combine a number of these inharmonic overtones, it tends to sound “noisy.” Non-fundamental tones that are multiplied by fractional amounts—not whole numbers—are called partials.

In summary, harmonics are a type of overtone that are whole-number multiples of the fundamental frequency, while overtones are any partial higher than the lowest partial in a compound tone.