The standard unit of frequency in the International System of Units (SI) is the hertz (Hz).

Frequency is defined as the number of cycles or oscillations that occur per unit time. This fundamental concept in physics is crucial for describing a variety of phenomena, including sound waves, electromagnetic waves, and atomic vibrations. Specifically, one hertz (1 Hz) corresponds to one cycle per second. For instance, when we say that a sound wave has a frequency of $440 \, \text{Hz}$, it indicates that the wave completes $440$ cycles each second.

The term “hertz” honors Heinrich Hertz, a German physicist who was the first to provide experimental evidence for the existence of electromagnetic waves. The hertz is widely utilized across various scientific and engineering fields, including radio and television broadcasting, telecommunications, and electronics. Additionally, it plays a role in everyday life, such as in the measurement of musical note frequencies and the operational speed of computer processors.

Beyond the hertz, there are several other units of frequency that are commonly used, including kilohertz (kHz), megahertz (MHz), and gigahertz (GHz). These units are typically employed to describe higher frequencies, such as those prevalent in radio and microwave communications. Nevertheless, the hertz remains the primary unit of frequency within the SI system.