Yea, OK. I guess this is a thing now. Remember back in the Gingerbread days, as well as the Ice Cream Sandwich/Jellybean/KitKat days, they would go a couple years between whole number upgrades to Android? I guess not anymore.
There are three major stories here. One is that Android M officially stands for Android Marshmallow. Another is that the final developer preview was released today for Nexus 5, 6, 9, and Player. Finally, that Android Marshmallow will be Android 6.0.
Android 6.0 Marshmallow comes with a handful of great new features, most notably Doze. This keeps your device from using battery while it’s asleep. This is necessary for Android because it’s something that iOS devices have done for over a hundred years.
There’s also new features in Android 6.0 Marshmallow such as native fingerprint scanning support as well as Android Pay. There’s also some minor cosmetic changes, because mostly, this is a minor update.
Source: Android Developer’s Blog