All the Linux distributions are either derivative of GNU/Linux ( OS made up of Linux Kernel developed by Linus Torvalds and GNU software repository) or derived from other Linux derivatives.
Desktop distributions comes with Graphical user interface enabled by default & aimed at individual users and most of the administration work can be done using GUI. Good for new users and running Linux-based graphical applications.
Server Distribution are for more advanced users who are familiar with Linux command line as Graphical Interface is not enabled by default in most of the server distributions. Server distributions comes with web servers like apache and networking packages like DNS and useful for running backend services , work as web server or DNS Server.