Technically, Tartarus, a mythological hellish region deep beneath the earth, not connected with the Judeo-Christian concept of hell. Tartarus is where those who offended the (polytheistic) gods, went to be punished.
Correct. It was shorthand for those who don’t know their Greek mythology.
Back when I was a young whippersnapper, there were actually high school courses that covered Greek mythology. I even remember being introduced to it in grade school in the Fifties! Today you're lucky if some basic college humanities course covers even a part of it. I'm not sure if Bullfinch is still in print. Maybe they're using Graves, who does a fine job linking anthropology to mythology.
FReepers are among the most erudite people on the Internet, but I doubt most would know their Hades from their Tartarus, or their Styx from their Lethe. (Most people think Styx is a rock band.)
The word "hell" struck me as a barely acceptable sustitute for Tartarus. With so many Evangelicals on this site, that word resonates, even if it is not completely accurate.