Why does one sometimes refer to GNU/Linux instead of Linux?
Introduced by Richard M. Stallman in 1984, GNU is a project of operating system consisting solely of Free Sotwares. The Linux kernel, a creation which began in 1991, is the last component that has allowed to achieve an autonomous operating system solely composed of Free Software. GNU/Linux is thus the conjunction of the project GNU and the Linux kernel. It is this set which is distributed today by Debian, Mandrake, RedHat, etc.