Oh boy. Hell, Hades, Tartarus, and Gehenna. So these sort of are and sort of aren’t interchangeable terms - kinda - sometimes - maybe. If you’re familiar with Greek mythology, Tartarus is where Zeus and his brothers cast the Titans (particularly Chronos) into after they overthrow them; basically it’s a deep abyss of torment, and it comes up a few times in the exorcisms that were part of your entry into the catechumenate - it’s sometimes seen in older English versions interchangeably for Hell. Hades (which shares its name with the Greek god and its chief occupant) isn’t hell per se - imagine it like being in airport security for all eternity - it sucks, but it could certainly be much worse. Hades shows up in a handful of places in the New Testament, as it’s one of the closest Greek analogs to the concept being conveyed, i.e., Hell. We hear every Sunday that Christ descended into Hades, but that’s for another time. Gehenna has a rather nasty history and is where we get the notion of Hell as hot, as this is the place outside Jerusalem where the worshippers of Moloch offered burnt children as sacrifices, and which later became a place of burning all manner of things - from garbage to excrement.
Hell itself has a couple of different origins depending on who you ask, but there are arguments to be made for a connection to the Norse goddess Hel, as well as to a Proto-Indo European word meaning “covered” or “hidden;” both are probably just as likely. As all of these terms show up with some regularity (not to be too doom and gloom), you should generally understand all of them to refer to Hell as we might think of it, and obviously strive to avoid all of them. What we really need to know is that from the Orthodox perspective, we almost never deign to suggest who is or might be in Hell, and we understand that our eternal destiny, wherever it may be, depends entirely upon our response to God’s amazing love for us.