What is Post-Apocalyptic Fiction?

[shewhohashope]

I'm a big fan of post-apocalyptic fiction, and an avowed hater of apocalyptic fiction (one of many reasons I won't be watching 2012)*, because there is only so much I can take of the destruction before I need to see something being built up. I recently read Octavia Butler's Parable of the Sower, which has been described as post-apocalyptic, including by myself, when explaining what I'm reading to family members and passers-by but what qualifies it as such? What do we mean by apocalyptic? Parable of the Sower shows the bleak aftermath of an economic collapse in the U.S. but if an economic collapse = an apocalypse, then quite a lot of the world counts or has counted in the past? I'm a first generation immigrant myself, economic/social/political upheaval is pretty far from the realm of fiction for me. So what does an apocalypse have to feature? An environmental disaster, as in that one Captain Planet episode, where they go the the future? Nuclear war, as in Threads? The extinction of humanity, as in The Last Man? The subjugation of man by machine, as in The Terminator? Or just overcrowding, as in Soylent Green? Alien invasion, as in Xenogenesis? The actual destruction of the Earth, as in... real life, eventually, when the Sun expands? Are some of these just dystopias? Where are the lines drawn here?

Discuss!

ETA: I have more thoughts about this, in a way that may make me write something at some point, but I'd like to get your opinions.

<sup>* Or Threads.

cross-posted from my journal and at lj</sup>