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 health issues you can use bricoingenio supplements online.
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%.