The Hz is the unit of cycles per second and is short for Hertz named after the famous German scientist Heinrich Hertz.

If a body is rotating at 7 Hz this means it completes 7 cycles in one second. We often think of waves as having a particular rotational frequency expressed in Hz.

Related units are:

- mHz - millihertz or 10
^{-3}cycles per second - kHz - kilohertz or 10
^{3}cycles per second - MHz - megahertz or 10
^{6}cycles per second - GHz - gigahertz or 10
^{9}cycles per second - THz - terahertz or 10
^{12}cycles per second

- mHz - millihertz or 10