Wikipedia Reference

The hertz (symbol: Hz) is the SI unit of frequency. Its base unit is cycle/s (also called inverse seconds, reciprocal seconds). In English, hertz is used as both singular and plural. As any SI unit, Hz can be prefixed; commonly used multiples are kHz (kilohertz, 10³ Hz), MHz (megahertz, 10⁶ Hz), and GHz (gigahertz, 10⁹ Hz).

One hertz simply means one per second (typically that which is being counted is a cycle); 100 Hz means one hundred 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, or a human heart might be said to beat at 1.2 Hz. The frequencies of aperiodic events, such as radioactive decay, are expressed in becquerels.

To avoid confusion, periodically varying angles are typically not expressed in hertz, but rather in an appropriate angular unit such as radians per second. A disc rotating at 1 revolution per minute (RPM) can thus be said to be rotating at 0.105 rad/s or 0.017 Hz, where the latter reflects the number of complete revolutions per second. The conversion between Hz and rad/s is rad/s = 1Hz*2π.