A royal court or noble court is a place where an important ruler such as a king, prince or duke live. The building is often called a palace, but the “royal court” means not just the buildings but all the royal household (all the people who live and work there).
It is called a court because in early times the palace would have a court (an enclosed space) at the front.
In history there were great rulers who held important courts, e.g. Charlemagne.
People who work at court are “court officials”.