The Free On-line Dictionary of Computing (30 December 2018):

Mean Time To Recovery
MTTR

    (MTTR) The average time that a device will
   take to recover from a non-terminal failure.  Examples of such
   devices range from self-resetting fuses (where the MTTR would
   be very short, probably seconds), up to whole systems which
   have to be replaced.

   The MTTR would usually be part of a maintenance contract,
   where the user would pay more for a system whose MTTR was 24
   hours, than for one of, say, 7 days.  This means the supplier
   is guaranteeing to have the system up and running again within
   24 hours (or 7 days) of being notified of the failure.

   Some devices have a MTTR of zero, which means that they have
   redundant components which can take over the instant the
   primary one fails, see RAID for example.

   See also Mean Time Between Failures.

   (1998-05-01)