Frequency = total number × frequency. Frequency, also known as frequency, refers to the number of times that a number representing a certain characteristic appears in the variable value. According to the frequencies arranged in sequence, a frequency sequence is formed to illustrate the intensity of each group of marker values. The sum of each set of frequencies is equal to all units of the population. Frequency can be expressed in the form of tables and charts.

Frequency refers to the number of periodic changes per unit time, which is a quantity to describe the frequency of periodic motion. Usually represented by the symbol F or V, the unit is one second, and the symbol is S. ..

In order to commemorate the contribution of German physicist Hertz, people named the unit of frequency Hertz, abbreviated as "Hertz", and the symbol was Hertz. Every object has a frequency independent of amplitude, which is determined by the nature of the object itself and is called the natural frequency. The concept of frequency is not only used in mechanics and acoustics, but also in electromagnetism, optics and radio technology.