Plain-language answer: A decibel expresses a ratio on a logarithmic scale; by itself, dB does not specify an absolute power or voltage.
Why the definition matters
For power, 10 dB is a factor of ten, 3 dB is about double, and negative values indicate a reduction. Decibels make cascaded gains and losses easy to add.
Use the number correctly
State what is being compared, use the correct power or voltage formula and impedance assumptions, and keep sign conventions clear.
The common mistake
Calling a bare dB value a power level without a reference.
Measurement and safety boundary
Keep reference units, bandwidth, detector, direction, averaging, and test conditions attached to every number. Current regulator requirements and the complete installed system control RF-exposure compliance.
