One hertz simply means "one (event) per second"; 100 Hz means "one hundred (events) per second", and so on. The unit may be applied to any periodic event – for example, a clock might be said to tick at 1 Hz. The reciprocal of frequency is time (period); a frequency of 1 Hz is equivalent to a period of 1 second, a frequency of 1 MHz to a period of 1 microsecond. In older writings, e.g. pre-WWII articles about radio transmissions and its electronics, the older but similar unit cycles per second (cps) is seen, along with related multiples kilocycles, megacycles, and so forth.
