The Jargon File (version 4.4.7, 29 Dec 2003):

burn-in period
 n.

    1. A factory test designed to catch systems with marginal components
    before they get out the door; the theory is that burn-in will protect
    customers by outwaiting the steepest part of the bathtub curve (see 
    infant mortality).

    2. A period of indeterminate length in which a person using a computer is
    so intensely involved in his project that he forgets basic needs such as
    food, drink, sleep, etc. Warning: Excessive burn-in can lead to burn-out.
    See hack mode, larval stage.

    Historical note: the origin of ?burn-in? (sense 1) is apparently the
    practice of setting a new-model airplane's brakes on fire, then
    extinguishing the fire, in order to make them hold better. This was done on
    the first version of the U.S. spy-plane, the U-2.


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

burn-in period

   1.  A factory soak test intended to increase the
   chance that components that fail early due to infant
   mortality will fail before the system leaves the factory.

   2.  When one is so intensely involved in a new project
   that one forgets basic needs such as food, drink and sleep.
   Excessive burn-in can lead to burn-out.  See hack mode,
   larval stage.

   [Jargon File]

   (2007-01-17)