Wikipedia on rooting.
Rooting is the process by which users of Android devices can attain privileged control (known as root access) over various subsystems of the device, usually smartphones and tablets
You can install apps from other sources without root access on Android. But some may need those extra permissions to function.
Thanks for sharing, this was actually an interesting short read.
Since i was curious about the fee difference that caused so many to switch i did some digging and found this article. It also serves as a nice companion piece to highlight how Fidelity lowering their fees lead to Vanguard making those changes in the first place.
If i see this correctly the massive switch was to go from 0.12%-0.14% expense ratio in the Investor class funds to the cheaper 0.09% in the institutional class. And now everyone pays 0.08%.