Diffusion — noun — /dɪˈfjuːʒn/ /dɪˈfjuːʒn/ — the process of dispersing something broadly in every direction; the state of being dispersed in every direction (e.g., the diffusion of Marxist concepts).
In reverb and sound engineering, diffusion is the parameter controlling the dispersion and density of reflections in a reverberant signal, with low values producing sparser and more distinct individual reflections and high values yielding a denser, smoother, more uniform reverb tail.
In evidence accumulation models (cognitive psychology and neuroscience), diffusion denotes the stochastic component of the decision process that introduces moment-to-moment noise into the temporal accumulation of evidence.
P. L. Smith, R. Ratcliff, Psychology and neurobiology of simple decisions. Trends Neurosci. 27, 161–168 (2004), (available at https://doi.org/10.1016/j.tins.2004.01.006).
DIffuse it