Before we get into the nitty-gritty of what distribution (sometimes shortened to "distro") we're going to use, we must first take a rather large step backwards and consider the concept of Linux in a somewhat philosophical way.
A good description of "what Linux is" can be hard to pin down, due in no small part to a level of confusion willfully propagated by IT professionals, because it makes them sound much smarter than they actually are when they come to explain it.
Because you're reading this book, I'm going to assume that you know of Linux at a high level; you know that it's an operating system (OS) like Windows or macOS, that it's not seen much of the limelight, and that it's not generally used on the desktop.
This assessment is both right and wrong, depending on who you're speaking to.
Laid-back systems administrators (sysadmins) will lean back further, nod their 80s era mohawk, and agree that Linux is an OS—and a decent one at that. They will then go back to playing with whatever trendy software they're learning this week so that they can try and shoehorn it into the infrastructure next week.
Self-proclaimed graybeards will stop what they're doing, sigh audibly, and pick up their fourth cup of coffee before swiveling around to give you a lecture on the difference between GNU/Linux (or GNU+Linux) and the Linux kernel.
The lecture you receive will be tedious, will involve names such as Richard Stallman, Linus Torvalds, and possibly even Andrew Tanenbaum, and may even take upwards of an hour, but the main takeaway will be that Linux is the accepted name of the OS you're learning about, while also being technically incorrect. They will say that Linux is really just the kernel, and everything beyond that is a distribution wrapped atop the GNU tools suite.
It is considered sensible to avoid this debate at all costs.
