Decibels referenced to 1 mW.
In microwave and common carrier systems, a measure of power with reference to zero dBm at the Reference Transmission Level Point.
Power (dBm), measured at any transmission level point, can be expressed in dBmO by correcting the measurement for the difference in level between the point of measurement and the Reference Transmission Level Point.
In microwave and common carrier systems, circuit noise power measured with an instrument having psophometric weighting.
Psophometric is from the Greek psophos, meaning noise. Psophometric weighting is related to the interference effect of a 3kHz band of white noise with a power of -88 dBm.