Residence time

The residence time is 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 during which two particles are close to another (Ref. 1), but it can also be employed in other situations, such as in diffusion at interfaces.

References

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