Burn-in
Burn-in turns up in 2 fields: welding, statistics. Here is what it means to the people in each one.
Burn-in in welding
Shop word for how deeply a bead melts into the base metal or sidewalls, especially at the root and toes.
Informal term for fusion into the joint walls or previous passes, judged by eye, by the sound of the arc, or on a macro etch. Good burn-in means the arc dug into both sidewalls instead of piling metal on top. Too little leads to lack of fusion and cold lap; too much can cause undercut or burn-through on thin material.
"You're getting no burn-in on the sidewall, slow down and point the wire at the bevel."
Burn-in in statistics
Operating products under raised stress before shipment so weak units fail in the factory instead of in the field.
Burn-in runs every unit, often at raised temperature and voltage such as 125 C with the supply boosted above nominal, for hours to days, to flush out infant mortality failures. It pays off only where the hazard rate is falling, a Weibull beta below 1, and it uses up some of the useful life of the good units. Its cost in time, sockets and ovens drives a constant push to shorten or eliminate it once early failure rates drop.
"Burn-in fallout has been under 50 ppm for six months. Let's propose cutting it from 48 to 12 hours on this product."