mass density gradient, \(\bigtriangledown \rho\), \(\text{grad}\: \rho\)

https://doi.org/10.1351/goldbook.M03715

Change in mass density in a small distance divided by that distance.

Source:
PAC, 1996, 68, 957. 'Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)' on page 980 (https://doi.org/10.1351/pac199668040957)