It's a bit more than that.
Everything electronic has the possibility of failure. The actual chance of a failure in any period is "the probability of failure". When the period is a standard hour, then this probability of failure is expressed as a figure called MTBF or "Mean Time Between Failure" for repairable items and Mean Time to Failure for non-repairable items and is quite often in the millions of hours for static electronic units.
If this probability of failure is plotted against service life, there's usually an initial high probability for a time, known as the "infant mortality period"; then the probability of failure settles to a lower (hopefully much lower) value; then as the unit gets to the end of its life, the probability rises again. Electromechanical devices have distinct wear-out mechanisms, whereas "pure" electronic assemblies tend to wear out by odd things like moisture ingress into the packages, doping impurities migrating etc. These later mechanisms are mitigated by higher component quality and assembly techniques such as conformal coating.
"Burning-In" refers to a method of quality screening where the product is subjected to a brief, high stress, operating regime that simulates the actual service time relating to the infant mortality period. The idea is to weed out poor components and badly assembled units. The high stress is usually an elevated operating temperature, hence "burning-in". An incorrect burning in however can just serve to stress the units to destruction!