The term 'Unit of Acoustics' refers to two different units of measurement: the BEL (B) and the sone (S). The BEL is a unit of measurement for sound intensity, which is defined as the ratio of the sound pressure level to the reference pressure level. The sone is a unit of measurement for loudness, which is defined as the subjective perception of sound intensity. Both units are used to measure the intensity and loudness of sound in acoustics.