Answer:
The decibel is used to measure sound level, but it is also used in electronics, signals and communication. The dB is a logarithmic unit used to describe a ratio. It is no unit. The ratio may be power, sound pressure, voltage or intensity or several other things. Also units related to loudness like the phon and the sone have a connection to the decibel. Look at the link: "The Relation of Sound Quantities - their Levels and References".