I don't really understand.
It's the most recent season of the anime, simple as that. In fact two episodes have aired already, the most recent being Pikachu Dreams of Squishy.
XYZ is more like a "sequel" to XY, the previous season. There's more Pokemon and other things that weren't already in an episode. You can also watch some episodes on the official site if you're wanting to watch it.
Hope I helped :)