noise

https://doi.org/10.1351/goldbook.N04175
The random fluctuations occurring in a signal that are inherent in the combination of instrument and method.
Source:
PAC, 1989, 61, 1657. (Nomenclature for automated and mechanised analysis (Recommendations 1989)) on page 1663 [Terms] [Paper]
See also:
PAC, 1995, 67, 1745. (Nomenclature, symbols, units and their usage in spectrochemical analysis-XI. Detection of radiation (IUPAC Recommendations 1995)) on page 1750 [Terms] [Paper]