At any moment the market for gold — or any traded asset — holds two prices. The bid is the highest price a buyer is currently willing to pay; the ask (or offer) is the lowest price a seller will accept. A trade happens when the two meet. The 'spot price' you see quoted is usually the midpoint between them, a convenient single number for a two-sided reality.
What the spread tells you
The distance between bid and ask is the spread, and it is a direct readout of a market's liquidity. Wholesale gold is one of the deepest markets on earth — its spread is measured in cents per ounce. Physical retail products carry a wider spread, because minting, logistics, insurance and inventory risk all live inside it. The spread is not a trick; it is the visible cost of turning a bank-vault commodity into a coin in your hand.
Using both sides as an investor
Because you buy near the ask and sell near the bid, the round trip has a built-in cost — which shrinks, per gram, with product size and recognisability. This is why standard LBMA bars and world-famous bullion coins are the cheapest gold to own over time: their spreads are the narrowest. Before buying any product, it is fair to ask a dealer both questions: what do I pay today, and what would you pay me back? The honest answer to the second question is the real measure of a product's quality.