flux, $$J_{\text{X}}$$

of a quantity
https://doi.org/10.1351/goldbook.F02461
Flow rate of X through a cross-section perpendicular to the flow divided by the cross-sectional area.
Sources:
Green Book, 2nd ed., p. 65 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)
PAC, 1996, 68, 957. 'Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)' on page 974 (https://doi.org/10.1351/pac199668040957)