The fundamental frequency, often referred to simply as the fundamental, is defined as the lowest frequency of a periodic waveform. In music, the fundamental is the musical pitch of a note that is perceived as the lowest partial present. In terms of a superposition of sinusoids, the fundamental frequency is the lowest frequency sinusoidal in the sum of harmonically related frequencies, or the frequency of the difference between adjacent frequencies. In some contexts, the fundamental is usually abbreviated as f 0, indicating the lowest frequency counting from zero. In other contexts, it is more common to abbreviate it as f 1, the first harmonic. (The second harmonic is then f 2 = 2⋅ f 1, etc. In this context, the zeroth harmonic would be 0 Hz.)