The system that Linux uses to draw anything on the screen (showing the desktop, your windows, their contents, etc) is called a display server.
Linux has been using a display server called the X Window System (or x11) since its inception, but it's ancient and has limitations that can't be fixed without breaking everything that depends on it.
The Wayland compositor is the new display server that will be replacing x11, improving security and adding support for newer features like HDR. It's nearly ready for a full release now, and is already the default for some Linux distributions.