First of all, it's called BREAK-IN, it has NEVER been called burn-in. Bulbs/tubes/valves burn-in. Anything mechanical has a break-in period, from vacuum cleaners to automobiles and heavy equipment. It can be from 2 minutes on tweeters to a few hundred hours on heavy equipment. Bulbs, on the other hand, have a pass or fail burn-in period, usually around 24 hours. Electronics usually have an infant mortality rating. The more moving parts they have, the longer that period is. EX: a CD or actual HD vs a cell phone or a memory drive. You can usually get that type of information from the manufacturer of the product.
There are some products that have to be run-in, like brand new tires for a car, brake rotors and pads, or a stylus on a tone arm. In other words, they work better and perform as they were intended once they are "run-in" and begin their normal service life. You see drivers at races driving side to side to warm up the sidewalls, and wear the silicone off the tire face. It is also nice to see if the tread is going to peel off the tire casing, but not at 200mph with weight on it, vs checking the balance at 200mph.
Break-in has several components working together.
Run-in is a single component that has to wear to a certain point to work properly.
Burn-in refers to bulbs and filament/plate failure, or the actual bulb/glass burning through.
(A) Burn-out lives two houses down from me. His name is Pete the puffer.
Regards