What makes something bullion?
A product is bullion when its value comes from the metal itself. A one-ounce gold bar or an American Gold Eagle is worth its weight in gold plus a modest fabrication premium, nothing more, nothing less.
The opposite of bullion is numismatic or collectible product, where price depends on rarity, condition, and story. That market is real, but it is a different market, with different pricing, different liquidity, and much wider spreads.
Why do most buyers end up in bullion?
Bullion is the most transparent segment of the physical market: the spot reference is public, premiums are comparable across dealers, and buyback bids are easy to obtain. You always know roughly what you own and what it's worth.
Liquidity is the other reason. Recognized bullion, major government coins and refiner bars, can be sold to almost any dealer in the country on any given day, at a price you can estimate before you pick up the phone.
How does bullion show up in practice?
When a quote describes a product mostly by its weight and purity, one ounce.9999 fine, you're looking at bullion. When it leads with 'limited,' 'exclusive,' or 'first strike,' you're being shown something else.