dB abbreviation for decibel.
This is the scale used for indicating the relative magnitude of sound pressure level, other acoustical quantities or some other quantities relating to the flow of energy.

dB(A) means ‘A’ frequency weighted sound pressure level in decibels.
‘A’-weighting refers to a standardised frequency weighting used in sound measuring instruments. There is a known relationship between the overall ‘A’ weighted sound pressure level and the risk of industrial deafness. (see AS/NZS 1269.4:1998).

dB(C) means ‘C’ frequency weighted sound pressure level in decibels.
‘C’-weighting refers to a standardised frequency weighting used in sound measuring instruments. There is a maximum limit on the instantaneous exposure to peak sound pressure levels. This is given in terms of ‘C’ frequency weighted sound pressure level in decibels (i.e. 140 dB(C)).