tbf

from The Free On-line Dictionary of Computing (8 July 2008)

Mean Time Between Failures
Mean Time Between Faults
MTBF
TBF

   <specification> (MTBF, or "Mean Time Between Faults") The
   {average} time (usually expressed in hours) that a {component}
   works without failure.  It is calculated by dividing the total
   number of failures into the total number of operating hours
   observed.  The term can also mean the length of time a user
   may reasonably expect a device or system to work before an
   incapacitating fault occurs.

   See also {Mean Time To Recovery}.

   (1998-05-01)