What is Wayland?
Wayland is intended as a replacement for the X Window system with the aim to make it easier to develop and maintain.
Specifically, Wayland is the protocol used to talk to the display server to render the UI and receive input from the user.
Wayland also refers to a system architecture (more below), which will give you an understanding of how the protocol is used to build a working UI.
Wayland versus X Architecture? Call it a "Simplified X".
In an X setup, X clients talk to an X server and the server talks to a compositor. The comms between server an compositor is bidirectional.
The X Server also talks to the kernel. There is a critical interface called evdev (short for event device) which is the input event interface in the Linux kernel.
In Wayland - the display server and the compositor are rolled into one. The architecture is thus simpler.
