Trying to write a realistic fantasy world and I'm wondering what the difference between a princedom and a kingdom is? Is it just the name, or are there actual tangible differences? Also are there any real-life cases of princedoms I can draw from? I seem to remember there being one or two but I can't remember where.
My apologies if this assumption is incorrect, but based on stereotypes, I'm guessing your fantasy world is vaguely medieval/Renaissance European in flavor?
If so, then your primary model is probably the later medieval Holy Roman Empire, which has an emperor but very powerful lords of the individual territores. While Latin had a tendency to call everyone princeps, in German there's a pretty clear distinction between the emperor and the Fürsten (sing. Fürst)--princes.
In which case, the difference between a kingdom and a princedom is sovereignty. The princes are de facto rulers of their own territory, setting policies and running their government. At the same time, they're subject to (and part of the body making) imperial law. Ideally, princes in this schematic would not conduct foreign policy of their own.
That should give you enough to shape your world the way your plot wants it. ;)