There was a gold standard in the late 1800s into the early 1930s in the U.S. It backed the U.S. Government's issue of paper currency with a requisite minimum amount of gold the country kept in its coffers, in places like Fort Knox and in the teeth of its toothy presidents. The notion was that a loan or debt obligation had to be backed by something more than just a smile and a handshake, and the retention of gold was a key asset that the government wanted to use as its financial anchor in issuing paper with promises to pay back that amount in the future.
Along came the digital version of this gold—only today, digital gold currency can be issued by, well, pretty much anyone who can carry the trust of those plugging in to their systems. Companies and individuals can all issue digital, gold-backed currencies. The unit of gold in this system is a gram troy ounce, and exists as a kind of virtual global traveler's check, in that gold is generally accepted anywhere in the world as payment. And soon on Mars.