rotational diffusion

https://doi.org/10.1351/goldbook.R05410
A process by which the equilibrium statistical distribution of the overall orientation of molecules or particles is maintained or restored. Rotational diffusion may be compared to translational diffusion through which the equilibrium statistical distribution of position in space is maintained or restored.
Source:
Purple Book, 1st ed., p. 61 (http://old.iupac.org/publications/books/author/metanomski.html)