Hertz (Hz) is a unit of frequency, measured in s-1, or one over seconds. It is used to measure how many times something happens in a second. Hertz are an important unit for defining waves, where frequency is one of the defining characteristics.

A more specific unit, related to the Hz, is the RPM (rotations per minute). Two useful conversions: 1 RPM = 0.0167 Hz and 60 RPM = 1 Hz

Electrical grid

The electrical grid in North America and Japan runs at 60 Hz, while the European grid runs at 50 Hz.[1] This means that the voltage on the electrical grid hits its maximum value 60 (or 50) times in a second.