Frequency is the number of repetitions per unit of time, often referred to as the "time frequency" In physics and engineering: optics, radio and acoustics, the frequency is usually indicated by the Latin letter "f" or the Greek letter "v" (Nu). The frequency of a sine wave is the distance over which the waveform repeats. It is usually determined by taking into account the distance between the sequence of corresponding points of the same phase, such as zero transitions, ridges, depressions. As a rule, any wave pattern can be described under the conditions of sinusoidal components. For periodic waves, frequency has an inverse relationship with wavelength. The si unit of frequency is Hertz, the symbol is Hz, which is named after the German physicist Heinrich Hertz. The si unit of wavelength is a meter.