We normally differ between sound and noise.

 

In short, we normally refer to arranged, pleasant impressions as ‘sound’, while the more chaotic and obtrusive sounds are referred to as ‘noise’. There is a fine and individual line between ‘sound’ and ‘noise’.

Scientifically speaking, sound is defined in the following way:

“Elastic molecular fluctuations in the air or other media that create a chain reaction by putting the nearest particles in motion. The sound will then spread at a certain propagation velocity which is called the speed of sound in the medium in question.” 

Next: Frequency