Cycles per second
(and kilocycles, megacycles, etc.)

Cycles per second was an easy-to-understand measurement of the rate, or frequency, of audio and radio waves. It was renamed hertz (Hz) by international agreement in 1960, in honor of physicist Heinrich Hertz, with multiples kilohertz (kHz) and megahertz (MHz) replacing the KC and MC abbreviations previously found on radio dials. The new term was confusing to many at first, since the "per second" part was subsumed; you don't say hertz per second.