The LBMA, or London Bullion Market Association, is the trade body that underpins the world's largest over-the-counter gold market. It publishes the Good Delivery standard that defines the acceptable wholesale bar of nominally 400 troy ounces, accredits the refiners whose metal the market will take, and oversees the twice-daily benchmark auction known as the LBMA Gold Price.
Retail XAUUSD feeds are derived from this London OTC market, which is why gold liquidity is deepest and spreads tightest through roughly 07:00 to 16:00 UTC, and why benchmark auction windows can produce short bursts of volume on an intraday chart. Miners, refiners, exchange-traded funds and central banks settle physical contracts against the benchmark rather than against a broker screen price.