GRUB stands for the Grand Unified Bootloader, a program used to load and manage operating systems on a computer. It is commonly used in systems running Linux and allows users to select which operating system to boot when the computer starts. GRUB can handle multiple operating systems and provides a menu interface for easy selection. GRUB supports various file systems and can boot from different types of storage devices. It can also be configured to pass specific parameters to the operating system during boot, making it a flexible tool for managing system startup. Its versatility makes it a popular choice among developers and system administrators.