mass mean diameter

https://doi.org/10.1351/goldbook.15866
Diameter of a spherical particle with a mass equal to the mean mass of all the particles in a population.
Source:
PAC, 2007, 79, 1153. (Glossary of terms used in toxicology, 2nd edition (IUPAC Recommendations 2007)) on page 1255 [Terms] [Paper]