What Is the 'Spot Price' of Gold and Silver?

This is a partial reprise of a post from two years ago. The question has again arisen about the discrepancy between the spot price of gold and silver, and the prices shown on the front month of the futures market.

When you ask even an experienced trader, or even an economist who may have received a Nobel prize, 'What is the spot price, where does it come from, who sets it?' you will often