Kings, Kingdoms, Magnates (and the Pope)
A king is, well, you know, a king. A magnate is a noble similar to a king but that is subordinate to a king and who has some control over fiefs he does not own. Examples of magnates are Counts (or Comte in French), Earls, Princes and so on. Both kings and magnates may tax all the fiefs in areas they rule over (such as the Duchy of Normandy, which the Duke of Normandy does not own all the fiefs in.) While kings are basically very successful magnates, they are also considered "the anointed by God " to the common people.
A king has enormous wealth and power and can only be removed from that position if most of the active players owning fiefs in the kingdom vote to do so. These players "vote" the current population of their fiefs (10,000 population is 10,000 votes). This is done by calling a parlement (even the French had one, although it was not used as much as the English one). Any magnate can call a parlement to remove the king. Only the king can call the parliament for any other matter (like removing a title from a player.) Under some circumstances, a parlement is called to raise more money for the king.
The kings of France and England have special powers. These are: