-Hi-Fi: it stands for "High-Fidelity". It's a term used for high-quality audio back in the days when people still used records and magnetic audio cassette, but in today's digital-audio world the term doesn't really mean much anymore.
-Hi-End: means "high-end", simple refers to anything that's luxurious, good, and probably expansive. Using headphones for example, I would say low-end headphones are around $40-$1000, middle-range are around $1000-$3000, high-end are $3000+.
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"Every wise child in this world is sad and depressed."