The GNU Project was formed to develop a free Unix-like operating system, GNU. The existence of this system is our major accomplishment. However, the widely used version of the GNU system, in which Linux is used as the kernel, is often called simply “Linux”. As a result, most users don’t know about the GNU Project’s major accomplishment—or more precisely, they know about it, but don’t realize it is the GNU Project’s accomplishment and reason for existence. Even people who believe they know the real history often believe that the goal of GNU was to develop “tools” or “utilities”.
To correct this confusion, we have made a years-long effort to distinguish between Linux, the kernel that Linus Torvalds wrote, and GNU/Linux, the operating system that is the combination of GNU and Linux. The resulting increased awareness of what the GNU Project has already done helps every activity of the GNU Project recruit more support and contributors.
Please make this distinction consistently in GNU software releases, GNU documentation, and announcements and articles that you publish in your role as the maintainer of a GNU package. If you want to explain the terminology and its reasons, you can refer to the URL http://www.gnu.org/gnu/linux-and-gnu.html.
To make it clear that Linux is a kernel, not an operating system, please take care to avoid using the term “Linux system” in those materials. If you want to have occasion to make a statement about systems in which the kernel is Linux, write “systems in which the kernel is Linux” or “systems with Linux as the kernel.” That explicitly contrasts the system and the kernel, and will help readers understand the difference between the two. Please avoid simplified forms such as “Linux-based systems” because those fail to highlight the difference between the kernel and the system, and could encourage readers to overlook the distinction.
To contrast the GNU system proper with GNU/Linux, you can call it “GNU/Hurd” or “the GNU/Hurd system”. However, when that contrast is not specifically the focus, please call it just “GNU” or “the GNU system”.
When referring to the collection of servers that is the higher level of the GNU kernel, please call it “the Hurd” or “the GNU Hurd”. Note that this uses a space, not a slash.
For more about this point, see http://www.gnu.org/gnu/gnu-linux-faq.html.