Sound is the wave of air molecules caused by the motion of an object. It is the vibrations that travel through the air or another medium and can be heard when they reach a person's or animal's ear. Sound is a sequence of waves of pressure that propagates through compressible media such as air or water. (Sound can propagate through solids as well, but there are additional modes of propagation). During propagation, waves can be reflected, refracted, or attenuated by the medium.
decibel (dB) = 1/10 of bel (B) and neper