Noise level

In telecommunication, noise level is the noise power, usually relative to a reference.

Note: Noise level is usually measured in dB for relative power or picowatts for absolute power. A suffix is added to denote a particular reference base or specific qualities of the measurement. Examples of noise-level measurement units are dBa, dBa(F1A), dBa(HA1), dBa0[?], dBm, dBm(psoph), dBm0[?], dBm0P[?], dBrn, dBrnC[?], dBrn(f ₁ - f₂), dBrn(144-line), pW[?], pWp, and pWp0.</b>

Source: from Federal Standard 1037C and from MIL-STD-188