Thrash Metal: An euphemism for the musical genre "Trash Metal" that became the norm in the name of marketing and political correctness. The original term "Trash Metal" though reflecting well the reality of that particular genre (trash content) had to be replaced because it was considered insulting by the barbarians, rednecks, sociopaths and other musically illiterate people who listen to it.
The term "Thrash" was selected by the music industry to replace "Trash" mainly for 2 reasons:
1. The similarity of the 2 words can be exploited by modern search engines like google. Regardless using "Thrash" or "Trash" google algorithm will understand what you are looking for and deliver the content.
2. The heavy shredding-style guitar work characterizing the genre is associated in the barbaric mind of the people listening to it with "thrash action".
People with significant music education disregard the trend and keep using the term "Trash Metal" .... which is content-wise correct.