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MTTR
From Wikipedia, the free encyclopedia
MTTR is an abbreviation that has several different expansions, with greatly differing meanings. It is wise to spell out exactly what is meant by the use of this abbreviation, rather than assuming the reader will know which is being assumed. The M can stand for any of minimum, mean or maximum, and the R can stand for any of recovery, repair, respond, or restore. The most common, mean, is also subject to interpretation, as there are many different ways in which a mean can be calculated.
Mean time to repair
Mean time to recovery/Mean time to restore
Mean time to respond
Mean time to replace
In an engineering context with no explicit definition, the engineering figure of merit, mean time to repair would be the most probable intent by virtue of seniority of usage. It is also similar in meaning to the others above (more in the case of recovery, less in the case of respond, the latter being more properly styled mean "response time").

Mean time between failures
From Wikipedia, the free encyclopedia

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Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a system during operation.[1] MTBF can be calculated as the arithmetic mean (average) time between failures of a system. The MTBF is typically part of a model that assumes the failed system is immediately repaired (MTTR), as a part of a renewal process. This is in contrast to the mean time to failure (MTTF), which measures average time to failures with the modeling assumption that the failed system is not repaired (infinite repair rate).
The definition of MTBF depends on the definition of what is considered a system failure. For complex, repairable systems, failures are considered to be those out of design conditions which place the system out of service and into a state for repair. Failures which occur that can be left or maintained in an unrepaired condition, and do not place the system out of service, are not considered failures under this definition.[2] In addition, units that are taken down for routine scheduled maintenance or inventory control, are not considered within the definition of failure.

What does MTTE stand for?
Mean Time to Error

Source:  Wikipedia