Sweet, here's a quick explanation! RPM is a package management system (the thing that keep tracks of all your installed applications and their dependencies). Distros which use RPM are commonly bundled together as "RPM-based". Examples include fedora, RHEL (Red Hat Enterprise Linux), Alma Linux, Rocky Linux, Oracle Linux and openSUSE to name a few! :3

WM stands for window manager, it's an application which only job is to keep track of all your application windows, their position on the screen and their state (minimized, open, etc.). Examples include i3wm (which is what I'm using), Kwin, mutter just to name a few!

DE stands for "Desktop Environment", which is a bundle of a bunch of different applications. A DE comes with bundled with both a window manager, but also stuff like application launchers, notification handlers, toolbars, file browsers, etc. Some common ones are GNOME (which ships with mutter for window management), KDE (which comes with the Kwin window manager) and XFCE (which uses the xfwm4 WM).

When it comes to a base fedora install you can either install the regular fedora desktop (which comes with the GNOME desktop environment) or you can install one of their "spins" which is fedora but with other DE/WM choices. You can read more about that here: http://spins.fedoraproject.org/ You can also switch DE/WM after you're done installing, too :)

So in short a DE is a pre-packaged solution which includes all the utilities and tools to make your experience more smooth and integrated, including a window manager. Meanwhile a WM is either bundled with a DE or installed standalone (like i3wm), and when it's installed standalone it allows for a more customized and personalized workflow, where you as the user dictate which utilities you want to use.

I hope this cleared up some confusion! ^^ let me know if you have more questions, I love talking about this stuff! :3