If I have built all sorts of crap on my map, but want to revert it back to fresh and unedited, could I extract the seed and make a new world with that seed? Effectively rerolling the same world, but without all my changes?
It's the number which your map is generated based off of. When you first make a new map (or rather new level.dat) the game makes a random number, then anytime you encounter new chunks the terrain generator runs it through some fancy calculations to build the world.
The seed is a single small number that tells exactly what your whole (unedited) world looks like! Until the world generation engine is updated again, that is. :smile.gif:
Basically, the seed is a number that tells the random number generator where to start at. That way, if you use the same seed, all the "random" choices and decisions of the game generator end up being the same as before.