A BootLoader is the first software program that runs when a computer starts. It is loaded by the BIOS at the end of hardware initialization and is responsible for loading the OperatingSystem Kernel and transferring control to it.
A multiboot loader offers a menu and the ability to select from a list of operating systems. Multiboot loaders include:
You can chain BootLoaders, eg. GRUB can load up Windows' BootLoader (this is the preferred method for DualBooting Linux and MicrosoftWindows.)
There's also a strange beast called LoadLin.
11 pages link to BootLoader: