Power Spectral Density (PSD).
Power Spectral Density (PSD). The amount of an emission's transmitted carrier power applied at the antenna input falling within the stated bandwidth. The units of power spectral density are watts per hertz and are generally expressed in decibel form as dB(W/Hz) when measured in a 1 Hz bandwidth, dB(W/4kHz) when measured in a 4 kHz bandwidth, or dB(W/MHz) when measured in a 1 MHz bandwidth.
47 CFR § 25.103
Terms with definitions including the (RR) designation are defined in the same way in 2.1 of this chapter and in the Radio Regulations of the International Telecommunication Union.