GNU/Linux Ubuntu Fixing GRUB Guide
Hi! The Tutorial Shows You Step-by-step How to Reinstall/Fix GRUB 2 in Ubuntu GNU/Linux.
And GNU GRUB for Ubuntu Linux is a very powerful Boot Loader, which can load a wide variety of Free Operating Systems, as well as Proprietary OSes with Chain-loading.
And a Boot Loader is responsible of loading and trasferring control to a Kernel OS Software (such as Linux or GNU Mach).
The Kernel, in turn, initializes the rest of the Operating System (e.g. a GNU system).