The unit of measurement for frequency in the SI system is the hertz (Hz). It represents one cycle per second and is used to quantify oscillations, waves, and other periodic phenomena. Frequency is significant in various fields, including physics, engineering, and music, as it relates to how often a repeating event occurs over a specified time interval. For instance, sound waves are characterized by their frequency, affecting pitch, while electromagnetic waves are also defined by their frequency, impacting their energy and wavelength.