1. A relative measurement based on a fixed value equating 0dB. (Ex: 0db SPL equals the threshold of hearing)
2. A non-linear scale used to define differences in analog voltages, acoustic sound pressure, and amplifier wattage.
3. A value based on 1/10th of a Bel (a measurement defined and named after Alexander Graham Bell). This is why the “B” is always capitalized “dB”.