The fall also, in mythological terms, refers to the expulsion of Lucifer Morningstar from Heaven after his rebellion against God.
Most variants of this myth have Lucifer refusing to bow to God's will in light of one development or another, usually involving humanity. One interesting variant of this muth has Lucifer rebelling not out of pride but out of love. When ordered to leave Heaven, and God's presence, for all eternity in order to serve humans, Lucifer finds that his love for God is so great that he cannot comply, and so was cast out.
Here, again, there is a divergence of stories. In some myths, other angels simply packed up and left Heaven with Lucifer. In others, Lucifer lead a revolt against God, and the War divided the angels, with Lucifer still losing.
After leaving Heaven, Lucifer fell for a very long time. Hell's existence prior to this is another cloudy subject. Either it pre-existed (God being omniscient) or Lucifer's Fall caused it to spring into existence. In any event, it was a highly unpleasant place, but he was rather stuck with it.
According to most Christian theology, Lucifer, now Satan, the Enemy, will reign in Hell forever. Of course, that kind of puts the kibosh on the idea of an infinitely forgiving God, but perhaps Lucifer will become Morningstar again.