What is "dB"?
dB or decibel is a relative unit for the quantification of the audio level or audio level change. As it is based on a logarithmic scale, it more or less indicates levels as perceived by the human hearing. Each unit of the dB-scale represents a factor. A factor of 2 equals 6 dB for amplitude values (sound pressure, voltage, current) and 3 dB for any power related measures.
By adding a reference, the dB-scale can apply to absolute values, like 94 dB re 20μPa (which in this case is the same as 1 Pa).