The Gold-Silver Ratio represents how many ounces of silver it takes to buy a single ounce of gold. Today the ratio floats, since gold and silver prices are adjusted daily by market forces, but this wasn't always the case. The ratio has been permanently set at different times in history - and at different places - by governments seeking monetary stability.
Trading the Gold-Silver Ratio makes sense for those worried about devaluation, deflation and currency replacement. Precious metals have a proven record of maintaining their value in the face of any contingency that might threaten the worth of a nation's fiat currency.