The X Window System is not installed by default, but is available in the FreeBSD ports collection. Wayland is also available for FreeBSD (unofficially supported).
The X Window System and Wayland are both graphical user interface (GUI) systems, but they have different underlying technologies. The X Window System is a legacy system that is not included by default on FreeBSD, while Wayland is an alternative GUI system that is available for FreeBSD.