Mean time (to) first failure (MTFF, sometimes MTTFF) is a concept in reliability engineering, which describes time to failure for non-repairable components like an integrated circuit soldered on a circuit board.
[1] For repairable components like a replaceable light bulb the concept of mean time between failures is used to describe the failure rate.
The key is that this is a non-repairable and non-recoverable failure.
However, if this failure was due to a burned out integrated circuit that circuit itself can't be repaired and must be replaced.
It's generally used to predict the first failure after manufacturing [2][3]