failure rate (λ)

The fraction of a population that fails within a specified interval, divided by that interval.

NOTE 1  Standard methods of reporting failure rates of semiconductor devices include 1) percent failed per 1000 hours and 2) FITs.

NOTE 2 The interval may be expressed in operating hours, storage hours, operating cycles, or other units of interval measurement.

NOTE 3 Typically, the term "failure rate" means the instantaneous failure (hazard) rate.

NOTE 4 The statistical upper limit estimate of the failure rate is usually calculated using the χ² (chi-squared) function.

References: 

JEP122C, 3/06
JESD74A, 2/07
JESD91A, 8/01