Indicators of reliability and maintenance frequency of the equipment. There are several different ones: MTBF = « Mean Time Between Failure », or « Average Time of Well-Functioning » = Average time between two breakdowns.
It is an indicator used to measure the performance of the maintenance and the reliability of equipment and the MTTR= « Mean Time To Repair », or » Average Total Time of Repair » or even average time to repair, a second indictor to measure the efficiency of the maintenance.