Standardized adaptation of objective sound level measurements
(unit: dB) to a normal person's subjective  sound sensation (unit: dB (A)). This adpatation is used to approximately evaluate  the human ear’s actual response to a specific sound event. Generally, measurement devices already apply A-weighting, but if this is not the case, A-weighting can be applied later using standard values. 

Materials and/or structures designed for sound absorption
(see "Absorption"). Most commonly used are porous (e.g. foams) or fibrous (e.g. rock wool) materials for the absorption of air-borne noise, and viscoplastic materials glued to solid structures for the absorption of solid-borne noise (see "Solid-borne noise").

Reduction ("attenuation") of sound through its more or less complete conversion to another form of energy (mainly heat).See also: "Dissipation". 

A measure of the sound-absorptive property of a material.

A room the inner surfaces of which are covered with sound absorption materials in order to (almost) completely eliminate the reflection of sound waves. A more precise term is "anechoic room".

General: the science of sound. Subspecialties: technical acoustics,  room acoustics, musical acoustics, medical acoustics, etc.

Part of the sound energy of sound waves propagating through the air is absorbed by the vibration of air molecules induced by the sound waves (depending on temperature and relative humidity).

Air-borne noise is a sound-wave that is transmitted through the air
(in contrast to fluid- or solid-borne noise).

Reduction of the air-borne noise using noise-absorbing materials
(see "Absorption").

Barrier (see insulation) to the propagation of air-borne noise, through encapsulation of the sound source, construction of sound protection cabins for persons, noise insulation walls between rooms etc.
Important factors are the mass, stiffness resp. flexibility, impermeability and dimensions of the barriers used.

See "Absorption"