Though “GNU/Linux” (or “GNU+Linux”) is the most accurate term for the combination of the GNU operating system and the Linux kernel that is the foundation for many free & open source platforms, many people colloquially refer to this and the collection of software placed atop it as just “Linux”.
These collections of software are comprised of vast pre-selected sets of tools, applications, libraries and documentation along with (but not always) a desktop environment layered upon that GNU/Linux base. Quite often the communities or projects that maintain these sets of software brand them as unique Linux operating systems and make them available to people as “Linux distributions”.
There are a multitude of Linux distributions available to download, try and install by people and they can be configured for general use or be narrowed right down for specific tasks, which of course means there are hundreds of them out there as alternatives to each other and to proprietary operating systems.
A “Free & Open Source” Alternative
Though Linux is best known as server or infrastructure operating system, it also exists as a free and open source alternative to Apple macOS and Microsoft Windows for use on everyday computers, such as laptop and desktop PCs, and like these operating systems Linux is available with a graphical user interface and other software you are accustomed to using.
However to be “free and open source” means adopting not just a different development process but a whole set of core principles that differs from proprietary software (as found in operating systems like Apple’s macOS, Microsoft Windows and others). To be “open source” means to develop completely openly—all source code is freely available to the public so that to anyone can view, edit or contribute to it—and “free” here refers not to the cost of the software but to its liberty—as no one entity owns the software it essentially belongs to everyone, without restriction.
So, in part, making the switch Linux is an ethical decision about the software you use on a daily basis and the rights you and others have to the information and things you use.