/grēn līt-niŋ/
[IBM]
n. 1. Apparently random flashing streaks on the face of 3278-9 terminals while a new symbol set is being downloaded. This hardware bug was left deliberately unfixed, as some genius within IBM suggested it would let the user know that 'something is happening'. That, it certainly does. Later microprocessor-driven IBM color graphics displays were actually *programmed* to produce green lightning!
2. [proposed] Any bug perverted into an alleged feature by adroit rationalization or marketing.
"Motorola calls the CISC cruft in the 88000 architecture 'compatibility logic', but I call it green lightning".
See also feature.