In a GNU/Linux system, Linux is the kernel component. The rest of the system consists of other programs, many of which were written by or for the GNU Project. Because the Linux kernel alone does not form a working operating system, we prefer to use the term “GNU/Linux” to refer to systems that many people casually refer to as “Linux”.
People who know they are using a system that came out of the GNU Project can see a direct relationship between themselves and GNU. They won't automatically agree with our philosophy, but at least they will see a reason to think seriously about it. In contrast, people who consider themselves “Linux users”, and believe that the GNU Project “developed tools which proved to be useful in Linux”, typically perceive only an indirect relationship between GNU and themselves. They may just ignore the GNU philosophy when they come across it.
I use the following software on GNU/Linux: