| 1. a decrease between two points of an electric, electromagnetic or acoustic power|
2. the quantitative expression of a power decrease by the ratio of the values at two points of a power or of a quantity related to power in a well defined manner
NOTE 1 – By extension the words "attenuation" or "loss" may represent the ratio of powers in a given situation and in a reference condition; for example "insertion loss".
NOTE 2 – Although the term "loss" is not synonymous in English with "attenuation" in every context, it is used to express the ratio of two powers in certain specified conditions as for example in "insertion loss" and "return loss", equivalent in French to "affaiblissement d'insertion" and "facteur d'adaptation" respectively.
NOTE 3 – Attenuation is generally expressed in logarithmic units by a positive value.