A gem is a physical object which can be converted directly to Shmuckers by a caster, warlord or ruler. Shmuckers cannot be made into gems, except by a Moneymancer.
Well, that's cool. New info for us. There's no third party buying gems, it just poofs from gem to shmuckers. But...
Note that Rob used the term Ruler. He found the term did not have a page on the Wiki, instead finding us using "Overlord".
Here's why, I think... Klog 5. "Only one overlord per side. Overlord sets production for all cities."
Later, we have Klog 10. Gone is the term Overlord, now it's Ruler. "Some may disobey if the believe the order goes against higher orders or the Ruler's interests."
So, this is what I think we were supposed to believe. Parson first met Stanle, an Overlord. He lacked knowledge of Royals, so had no reason to know that Overlord wasn't the term for all Side leaders. No, he later finds out Overlords are non-Royal side leaders, and Royalists call themselves Kings (or Tsar, or Don, or something else). So he now uses the term Ruler to refer to a Side's leadership, regardless of Royalty. We, however, don't get in on that insight, and so it looks like Ruler and Overlord are interchangeable.
So, hopefully Rob will clarify. If Ruler is correct, I'll fix the Wiki, if no one beats me to it.