I can do you one better. In short, it's about standardized Linux. Kinda like the E. Pluribus Unum of myriad Linux distros (no pun intended).
Shakespeare to French, right? "...pourquoi êtes-vous Romeo?"
From Michael Stutz, the author of "The Linux Cookbook: Tips and Techniques for Everyday Use"
It takes more than individual software programs to make something that we can use on our computers -- someone has to put it all together. It takes time to assemble the pieces into a cohesive, usable collection, and test it all, and then keep up to date with the new developments of each piece of software (a small change in any one of which may introduce a new software dependency problem or conflict with the rest). A Linux distribution is such an assemblage. You can do it yourself, of course, and "roll your own" distribution -- since it's all free software, anyone can add to it or remove from it and call the resulting concoction their own. Most people, however, choose to leave the distribution business to the experts.
For the purposes of this book, I will assume that you are using the Debian GNU/Linux distribution, which, of all the major distributions, is the only one designed and assembled in the same manner that the Linux kernel and most other free software is written -- by individuals.
And when I say "Linux" anywhere in this book (including in the title), unless noted, I am not referring to the bare kernel itself, but to the entire working free software system as a whole. Some people call this "GNU/Linux."(8)
There are many other distributions, and some of them are quite acceptable -- many users swear by Red Hat Linux, for example, which is certainly popular, and reportedly easy to install. The SuSE distribution is very well-received in Europe. So when people speak of Debian, Red Hat, SuSE, and the like in terms of Linux, they're talking about the specific distribution of Linux and related software, as assembled and repackaged by these companies or organizations (see Linux Resources on the Web). The core of the distributions are the same -- they're all the Linux kernel, the GNU Project software, and various other free software -- but each distribution has its own packaging schemes, defaults, and configuration methods. It is by no means wrong to install and use any of these other distributions, and every recipe in this book should work with all of them (with the exception of variations that are specific to Debian systems, and are labelled as such in the text).
In Debian's early days, it was referred to as the "hacker's distro," because it could be very difficult for a newbie to install and manage. However, that has changed -- any Linux newbie can install and use today's Debian painlessly.
NOTE: I recommend Debian because it is non-corporate, openly developed, robust (the standard Debian CD-ROM set comes with more than 2,500 different software packages!), and it is entirely committed to free software by design (yes, there are distributions which are not).