Mainline Kernel

To quench the hunger of people waiting in between stable releases for testing their hardware features and software improvements, Linus Torvalds himself has implemented the concept of Mainline Kernel that will be in between prepatch(RC-Release candidates) and the stable releases that can be considered short term stable releases for testing.

This will last for 2-3 months before it moves to stable one, for now 4.10 is considered to be in that mode!. More about this in the Kernel releases page.