Magic Smoke is a slang term in electronics that describes the gasses that escape a component when the incorrect polarity or amount of electricity is supplied.
#Examples that you should never try yourself!
You should never intentionally try to create magic smoke. Let's reiterate that. DO NOT TRY THIS YOURSELF. With that caution in mind, it is instructive to see what magic smoke looks like for different components.
The YouTube channel Afrotechmods has a smoking compilation of component failures where you can safely view the various catastrophic failures and magic smoke of some of your favorite components.