A Fair Value Gap is a three-candle pattern where price moved so fast that it left a price range traded on only one side. On the chart it looks like a gap between candle 1's wick and candle 3's wick, with candle 2 being a big displacement candle.
Price often returns to "rebalance" that gap before continuing, and that return is the entry. The full lesson covers exact rules, the 50% level, which gaps to skip, and complete entry, stop and target rules.