boot loader
also: bootloader, boot program, first-stage loader
A program that runs before the operating system kernel, responsible for loading the Linux kernel into memory and passing control to it during system startup.
The boot loader is the first software that executes when your computer powers on. It lives in a special area of your disk (like the Master Boot Record or UEFI partition) and initializes hardware, then locates and loads the Linux kernel into RAM.
Common Linux boot loaders include GRUB (Grand Unified Bootloader) and LILO (LInux LOader). GRUB is the modern standard on most distributions and provides a menu to choose between multiple operating systems or kernel versions.
Example: When you turn on your computer, the boot loader runs first, displays a menu showing available kernels, and after you select one (or waits for a timeout), it loads that kernel and hands off control. Without a boot loader, the CPU wouldn't know how to find and start Linux.