Over the weekend I heard an acquaintance mention something called "monoatomic gold", followed by a bevy of fantastic and surprising claims about the substance, what it does, and how it was discovered. 

My subsequent Google searching has returned a lot of pages with mysticism and conspiracy theories, but not much by way of solid definition.

What is "monoatomic gold"? What is it claimed to do? Is there any scientific validity or study behind those claims?