relaxation time

The term relaxation time is the time for some process to return to its normal/equilibrium state (relaxation). The term is often used for a quantification of this time in cases where the return is characterized by some quantity falling off exponentially. This is the typical case for the overall relaxation that is a composite of the relaxations of many individual items (e.g., molecules, atoms, or other particles). Relaxation time is the time for that quantity to fall by a factor of e. The return-to-normal's half-life carries the same information but scaled to the time in which the quantity halves.