Ruling Princes are the rulers of the princedoms; they bow only to the High Prince and Lady/Lord of Goddess Keep. As long as they don't interfere with other princedoms' rulings or any agreed upon laws of the Continent they hold absolute dominion over their princedom. This title passes to a son, usually the oldest legitimate son.
A Prince's duty is to protect his people. In return for his protection the athr'im supply his Keep with food and goods. During the Rialla the Prince trades for items that his athr'im need from other princedoms. Every three years the Princes meet with the High Prince and each other at the Rialla. Only ruling Princes are allowed to participate in formal assemblies at the Rialla. Also, the ruling Princes stand and walk alone as the sole rulers of their lands - this tradition was broken in the Rialla of 698, when Rohan walked into the Lastday banquet with Sioned at his side, which fairly screamed that she would share in his power.
A Prince is born to a ruling Prince and may or may not be the heir to the princedom. Should the ruling Prince be named after an heir's birth, then that heir also becomes a Prince (such is the case with Kostas). An informal address between Princes and/or Princesses is 'cousin.'
A Princess is either the wife or daughter of a ruling Prince. In recent times Princesses have been heiresses, through which the royal line runs. In these cases (such as with Gemma) the Princess must stand beside her husband as they are confirmed as rulers of their princedom.