Hz is for Hertz, the frequency or cycles per second.
In other words, the speed of the clock, or the speed of the twisting.
In general terms, a frequency of 1 hertz means that something happens once a second, but in the
nodeeditor program, the speed may be faster or slower. So it is the relative speed.

Examples:
Hz = 0.1 is slow twist...
Hz = 5 for faster twist...
- Brian

The frequency could be measured, but may vary depending upon computer?, software load? etc ?