This is the 13254th most frequent Russian word.
молния
Lightning.
In this sentence, 'молния' is used to denote a natural phenomenon, specifically a lightning strike.
Молния сверкнула на горизонте в темное небо.
A lightning struck on the horizon in the dark sky.
Here, 'молния' is referring to a zipper, demonstrating its use as a term for a clothing fastener.
Я поправил молнию на моей куртке перед выходом.
I adjusted the zipper on my jacket before leaving.
In this case, 'молния' is metaphorically used to refer to a quick flash or highlight visible on a screen or within television programming.