relative permittivity, \(\varepsilon_{\text{r}}\)

https://doi.org/10.1351/goldbook.R05273
Ratio of the electric field strength in vacuum to that in a given medium. It was formerly called the dielectric constant.
Source:
Green Book, 2nd ed., p. 14 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)