Unfortunately, due to some of the "issues" with artifacts produced by modern gear, HiFi has come to mean the opposite of what was originally intended. Some of these issues include cone breakup produced by hard membrane drivers, accentuated leading edges often caused by electronics and/or cables, a hard and glassy sound that can be caused by SS amplification devices, silver or silver plated wiring. Also, unnatural forwardness of presentation and emphasis on uppder midrange and lower high frequency ranges. And pretty much any artifact that produces listening fatigue.
However, it's also not clearly defined and some will call a good system with full frequency extension at the high end "HiFi" when it's simply not rolled off enough for the individual's personal tastes. Some have damaged hearing that includes a general reduction in high frequency hearing with the exception of sensitivity at certain frequencies, so they call anything that irritates their particular hearing issues as "HiFi". Folks with hearing damaged by headphone use or going to high-SPL concerts often enough perceive a more forward and aggressive presentation as more natural when others will call it "HiFi".
Personally, I don't think "HiFi" is a good term for any of this as it's being misused, but "the industry" is also partially to blame for selling a lot of gear that is, for better or worse... "HiFi".