It’s a tradition for the Battle for Wesnoth community to explain what our software version numbers mean to newcomers, since these often ask what’s the difference between the stable series, and the development series, and what happens when a new stable version is defined.
A simple answer addressing the difference between odd/even minor version numbers (i.e. Y in X.Y.Z) has usually sufficed, but now that we are producing releases for the 1.9 development series, misconceptions about the next major series (2.x) spread like the plague. I wrote a clarification post a couple of months ago, on the numbering scheme — since it’s getting lost in the depths of the Users’ Forum archive, I'll replicate it here for the few anonymous people who read this.
I’m also going to explain what’s the deal with this magic “2.0” version number, although that part is going to be a lot more subjective — in other words, I’ll address that subject from my own point of view instead of the development team’s.