A bootloader is a small program that runs before the operating system on a device, such as an iPhone. It is responsible for initializing the hardware and loading the operating system into memory. Checking the bootloader on an iPhone can be useful for troubleshooting issues or modifying the software on the device.
There are several ways to check the bootloader on an iPhone. One way is to use a software program such as iBoot or redsn0w. These programs can be used to check the bootloader version, unlock the bootloader, and even flash a custom bootloader onto the device.