Spot gold is the price of one troy ounce of gold for immediate settlement, formed in the over-the-counter bullion market centred on London rather than on a single exchange. The LBMA Gold Price auction, held twice each London business day, publishes the benchmark that contracts and valuations reference.
The XAUUSD quote shown on a retail trading platform is that spot price with the broker spread applied. This is why gold trades almost continuously from Sunday evening through to Friday evening, pausing only briefly around the New York close, rather than following equity exchange hours.
Spot gold differs from COMEX gold futures, which carry a fixed one hundred ounce contract size and an expiry date with a cost of carry premium, and from gold exchange traded funds, which are equity wrappers that trade in exchange hours and levy a management fee. Each route buys exposure to the same ounce with a different cost, leverage and settlement profile.