symmetry coordinate

symbols: $S_{i}$, $\boldsymbol{S}$
https://doi.org/10.1351/goldbook.08694
Each \(S_{i}\) is a linear combination of general coordinates, usually internal coordinates, constructed to take advantage of the molecular symmetry. The \(S_{i}\) are elements of the vector \(\boldsymbol{S}\). They have the same units as the general coordinates from which they were constructed.
Source:
PAC, 2021, 93, 647. (Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)) on page 766 [Terms] [Paper]