Jailbreak

This is the process by which full execute and write access is obtained on all the partitions of the iPhone. It is done by patching /etc/fstab to mount the System partition as read-write. This is entirely different to an unlock. Jailbreaking is the first action that must be taken before things like non-official activation, and non-official unlocking, can proceed.

The original jailbreak also included modifying the afc service (service used by iTunes to access the filesystem) to give full filesystem access from root. This was later updated to creating a new service (afc2) that allows access to the full filesystem.

Modern jailbreaks also include patching the OS kernel to get around code-signing and other restrictions.