All systems referred to as Linux today are, in fact, built on the work of this collaboration. Technically, the term Linux refers only to the kernel. Many programmers and contributors to GNU, including Stallman, argue emphatically that the full OS should be referred to as GNU/Linux in order to give credit not only to Linux but also to the GNU project and to highlight GNU’s goals of spreading software freedom—goals not necessarily shared by Linus Torvalds. Many others find this name cumbersome and prefer calling the system simply Linux. Yet others, such as those working on the Ubuntu project, attempt to avoid the controversy altogether by referring to GNU/Linux only by using their own project’s name.
Source of Information : Prentice Hall The official Ubuntu Book 5th Edition 2010