Those levels of radiated and conducted energy existing at a specified location and time when a test sample is deenergized. Atmospheric noise signals, both desired and undesired, from other sources and the internal noise level of the measuring instruments all contribute to the "ambient level".

The values of signals and noise that exist at a test location when the device under test is not active.

The level (of pollutant) in the general environment as characterized by an average over a suitably long time and large volume.