bootloader

An iPhone's bootloader is a small program stored in the phone's non-volatile memory that, as its name implies, loads the device's operating system.

The term bootloader has become popular because of jailbreaking, the act of hacking an iPhone to install third-party applications not sold via Apple's own App Store, which relies on pirated copies of the bootloader and operating system.

Historical perspective: According to Apple, "Jailbreak techniques use unauthorized modification to the copyrighted bootloader and OS, resulting in infringement of the copyright in those programs." For further discussion, see jailbreaking.