mean-time-to-failure (MTTF)

The average time to failure for components or nonrepairable systems.

NOTEThe MTTF is often the reciprocal of the hazard rate when the hazard rate is described by the Poisson or equivalent exponential function, e.g., in the constant or flat portion of the useful life region of the bathtub curve.

References: 

JEP122E, 3/09
JEP143B.01, 6/08