​Noise means any unwanted sound. Noise is not necessarily random. Sounds, particularly loud ones, that disturb people or make it difficult to hear wanted sounds, are noise. For example, conversations of other people may be called noise by people not involved in any of them; any unwanted sound such as domesticated dogs barking, neighbors playing loud music, portable mechanical saws, road traffic sounds, or a distant aircraft in quiet countryside, is called noise.

Acoustic noise can be anything from quiet but annoying to loud and harmful. At one extreme users of public transport sometimes complain about the faint and tinny sounds emanating from the headphones or earbuds of somebody listening to a portable audio player; at the other the sound of very loud music, a jet engine at close quarters, etc. can cause permanent irreversible hearing damage.

Sound intensity follows an inverse square law with distance from the source; doubling the distance from a noise source reduces its intensity by a factor of four, or 6 dB.​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​