mean time Average lifetime of a molecular, atomic, or nuclear system in a specified state. Note: For an exponentially decaying system, it is the average time for the number of molecules, atoms or nucl [..]

(Or mean lifetime, lifetime.) The average time during which anything can be said to reside within a specified region or to exist unchanged; for example, the mean life of a chemical species in the atmo [..]

The average time during which an atom or other system exists in a particular form.

Another way to say Mean Time Before Failure.