transport number, \(t\)

https://doi.org/10.1351/goldbook.T06489
Of ions B, the current density due to ions B divided by the sum of current densities of all the ions in the electrolyte. ISO recommends the name current fraction of ions B.
Source:
Green Book,2nd ed., p. 60 (https://www.cintegrado.com.br/site/documentos/green_book_2ed.pdf)