polarization, ζ in electrochemistry, in spectrochemical analysis

https://dx.doi.org/10.1351/goldbook.P04713
The difference of the electrode potential from the corrosion potential. The symbol should not be used for polarization.
Source:
PAC, 1989, 61, 19 (Electrochemical corrosion nomenclature (Recommendations 1988)) on page 21