Residence time

The typical time of permanence of a particle in a given environment. More precisely, the decay time $\tau$ that appears in the exponential decay $\exp(-t/\tau )$ at long times. Historically, the concept was introduced to describe the time a particle is close to another [1], but it can be employed in other situations, as in diffusion at interfaces.

References

1. R. W. Impey, P. A. Madden, and I. R. McDonald "Hydration and mobility of ions in solution" J. Phys. Chem. 87 pp 5071 - 5083 (1983)