In the AMMS;WE from
EXP a baron is a noble who owns the land he rules/administers/governs/runs roughshod over outright, instead of holding it from another.
A complication that many don't consider is the holding of mulitple titles. Baron George of Riverdeep may also be Duke of Courtwall, Earl of the North by North West Isles, and a Knight of the Wrist Band. All earned by himself or an ancestor for some reason or another. ("Drat it all, the Duke of Courtwall managed to get himself killed by his lover before we could get him drunk enough to have sex with a woman and produce an heir. Robert, would you like to be a duke as well as a baron?")
So Baron Robert (great grandfather of Baron George) finds himself -as Duke of Courtwall- an ally of a man he -as Baron- is having a border war with. If you think that's bad, they can get worse. A lot worse.
Add in a few generations of shifting alliances and animosities, along with additional rewards and the occasional divestment of title and priveleges, and keeping track of who is lord of where and squire of what can get a tad involved.
This all reminds me of a story I read long ago. In one part our hero is taken to a formal royal affair. When he arrives the aristocrats are being introduced. Each of which has about a dozen titles and honorifics bestowed for such things as making a killing in the market, writing the winning poem at a district poetry contest, or having the best kept vegetable garden. There are tons of them. After the last baron/count/earl/squire/knight is introduced come the lords. The lords are few in number, usually have done something momentous to earn the title, and where the barons/dukes/knights of something or other elicit barely a ripple of interest, the lords get everybody's attention. These are
important men.
In short, the power, prestige, and/or influence a noble has often depends on how he gained his title. What did he have to do to gain it? One easily gained will not have the cachet of an (officially) lesser rank earned through hard service. In addition, the power a title holds can depend on the society. In feudal Japan the nobility had little power, though they were, in theory, superior to the aristocrats who really ran the country. It is thought that the Japanese nobility were descended from the original immigrants from Korea, and kept pretty much 'pure' by breeding only among themselves. The aristocrats (daimyos and samurai for instance) arose from a mixture of Korean immigrant, Japanese aborigine and perhaps other groups as well, leading to a more 'vital' population than the inbreed nobility.
Finally, consider the variety of titles from around the world. Baron, bey, and boyar may be equivalent titles, but the power they held could vary wildly. But don't feel too bad. I thought a few hours of research on the Condylarthra would produce an essay for
Mythus Mutters. Only to learn that the Condylarthra as a group are on their way out -along with the other mammalian groups, to be replaced by four super groups based on work in genetics. (Did you know we're now grouped with bunnies and rats? In a group known as the Euarchontoglires. I learned this from an article in the April 2003 issue of
National Geographic) So I've got work to do before I can start my series on mammals for d20 games.
Good luck with your research.