Decibel

The decibel (dB) is a unit of measurement used to express the ratio of one value of a physical property to another on a logarithmic scale. When expressing power quantities, the number of decibels is ten times the logarithm to base 10 of the ratio of two power quantities. That is, a change in power by a factor of 10 corresponds to a 10 dB change in level.

For more information, see Wikipedia.