A fair value gap on gold is a three-candle imbalance in which the middle candle moves so rapidly that a band of price sees only one-sided trade. In the standard bullish definition the low of the third candle sits above the high of the first, and the bearish case mirrors it. On XAUUSD these form most frequently in the seconds after CPI, non-farm payrolls and FOMC decisions.
A gap is a candidate zone rather than an obligation: imbalances created by thin release-minute liquidity fill more often than those created by a genuine repricing of real yields or the dollar, which can remain open for weeks. Honest testing requires a fixed drawing rule, a defined invalidation, and a record that counts unfilled gaps as well as filled ones.