dB expresses a ratio between two numbers. Neither power nor voltage is implicit in the term. You have to explicitly state whether it is voltage, or power, or whatever.
If you say dBm then it's the ratio to 1 milliwatt. If you say dBV then it's the ratio to 1 volt, etc., etc. With that letter added you know if it is a ratio of power or voltage.
If I was twice as tall as somebody, it might be said I have a 3-dB height advantage ...
Ken
KE2N
Ken Jamrogowicz