Hertz is a unit of frequency that measures how many cycles of a periodic event occur in one second. It is commonly used in various fields, including physics and engineering, to describe sound waves, electromagnetic waves, and other oscillating phenomena. For example, a sound wave with a frequency of 440 Hertz corresponds to the musical note A above middle C. The term "Hertz" is named after the German physicist Heinrich Hertz, who made significant contributions to the study of electromagnetic waves in the late 19th century. His experiments helped lay the groundwork for modern telecommunications and radio technology. Today, frequencies are often expressed in kilohertz (kHz), megahertz (MHz), and gigahertz (GHz), which represent thousands, millions, and billions of Hertz, respectively.