Pure tone is a single frequency tone with no harmonic content (no overtones). This corresponds to a sine wave. It is characterized by the frequency - the number of cycles per second, the wavelength - the distance the waveform travels through its medium within a period, and the amplitude - the size of the cycles.
The Fourier theorem states that any periodic waveform can be decomposed as the sum of a series of sine waves with frequencies in a harmonic series and at specific phase relationships to each other.
Musical instruments usually generate tones composed of several sinusoidal waves with harmonic frequencies. The lowest of these frequencies (the fundamental frequency) determines the pitch of the tone, which is perceived by the human hearing. In music, notes are assigned to tones with different fundamental frequencies, in order to describe the pitch of played tones.
See also