Frequency is the number of times an event is repeated per second. It is measured in Hertz (Hz) – (cycles per second).
A leap year comes every 4 years. So the frequency of leap year is 12.6 Micro Hz.
1 Hz = 1 Cycle per Second
1 kHz = 1,000 Hz
1 MHz = 1,000,000 Hz
Human can able to hear only Acoustic range of audio frequencies, from 20Hz to 20kHz. This hearing range varies from person to person and it will decrease with age. If a sound system can handle this range, then people will not miss anything significant.
We can able to hear frequencies below 20Hz too, but it is difficult to tell that we are actually hearing those frequencies or our body is feeling those vibrations. For that we put a low end range of 20Hz, and frequencies below that will be taken as unimportant.