The term bullion refers to precious metals in bulk form that are regularly traded on commodity markets. The value of bullion is determined by the value of its precious metals content, which is defined by mass and purity.

The most common bullion is gold bullion. Gold bullion is pure gold. In many countries, the minimum purity is 99.5% for gold bullion bars and 90% for gold bullion coins. The typical purity for gold bullion bars is 99.9%. A higher purity is technically difficult to achieve.

Gold bullion that meets the defined minimum purity requirements is also called investment grade gold or just investment gold.