Wayland is a communication protocol that specifies the communication between a display server and its clients, designed to be a replacement for the X11 window system protocol and architecture.
I might be a little nitpicky here, but I feel it’s an important distinction to make as there is no single common Wayland server like Xorg is for X11.
A display server using the Wayland protocol is called a Wayland compositor, as it additionally performs the task of a compositing window manager.
Xorg on the other hand is basically one fat display server designed like a house of cards that everyone uses.