The term comes from repetitive phenomena such as sound waves having a frequency measurable as a number of oscillations, or cycles, per second.

[1] With the organization of the International System of Units in 1960, the cycle per second was officially replaced by the hertz, or reciprocal second, "s−1" or "1/s".

Other higher units like megacycle (Mc) and less commonly kilomegacycle (kMc) were used before 1960[3] and in some later documents.

[4] These have modern equivalents such as kilohertz (kHz), megahertz (MHz), and gigahertz (GHz).

Following the introduction of the SI standard, use of these terms began to fall off in favor of the new unit, with hertz becoming the dominant convention in both academic and colloquial speech by the 1970s.