Failure In Time (FIT) method of specifying component reliability.
The FIT rate is defined as the expected number of component failures per 10^9 (ten to the ninth power, or 1,000,000,000) hours.
The FIT rate can be converted immediately to the MTBF (Mean Time Between Failures) in hours as MTBF = 10^9/FIT.
The Annualized Failure Rate (AFR) can be calculated as AFR = (FIT * 8760)/109.
The advantage of using FIT rates rather than the MTBF metric is that FIT rates are additive.
For example, the FIT rate of a current-production M3F-PCIXD-2 interface is 200, the sum of the FIT rate of the fiber transceiver, 125, and the FIT rate of all other component failures, 75.
A FIT rate of 200 corresponds to an MTBF of 109/200 = 5M hours, and to an AFR of (200 * 8760)/109 = 0.00175 = 0.175%.