Originally Posted by Animor
Another question: "insecure boot" is the same as "unlocked bootloader"?
Insecure boot and unlocked bootloader do not refer to the same thing.
Insecure boot refers to the fact that a elevated permission root shell and root access is available by default for example for an insecure boot image when you start adb shell you will automatically see a root shell prompt of (You will also have acess to the ADB re-mount command which re-mounts the system r/w):
Where as on a secure boot image when you start adb shell you will automatically see a regular shell (And you will not have acess to the ADB re-mount command):
On a secure boot image you gain root access by rooting the device (Installing the su binary and some form of a Superuser app) and then you can obtain a root shell by either typing the following in either terminal or adb shell:
Which results in the familiar elevated privilege root shell:
An unlocked bootloader refers to the fact that you can modify any partition on the device without having to flash an officially signed firmware image. Let me know if you still have questions hopefully this clears things up for you