GRUB
Updated: 11/16/2019 by Computer Hope
Short for GRand Unified Bootloader, GRUB is a bootloader used for various Linux and other Unix-like operating systems. It resides on a primary disk partition. Like all bootloaders, GRUB is responsible for loading the operating system after POST (power-on self-test).
GRUB is developed and maintained by the GNU (GNU's Not Unix) project.