For the comics, please see Judgment Day (comic) and Judgment Day!.
Judgment Day was an ancient Human myth about the end of everything. It shared a common theme with Ragnarok and the Romulan Ganmadan. (PIC: "Et in Arcadia Ego, Part 2")
In 2378, Q described the upcoming court decision for his son as "Judgment Day for Junior". (VOY: "Q2")
In 2399, Cristóbal Rios compared Ganmadan to Ragnarok and Judgment Day, "an ancient myth". (PIC: "Et in Arcadia Ego, Part 2")
Judgement Day is a Christian concept.