Price gap
Untraded stretch between candle 1 and candle 3.
Candle 1 and candle 3 do not overlap in price — the stretch between them was never traded. The find becomes knowable at the close of the third candle.
Names
Neutral wording calls this a Price gap (German: Preislücke). ICT wording calls it a Fair Value Gap, short FVG (also Imbalance).
Settings
You can raise the minimum size so tiny gaps stay off the chart. Threshold measured against picks what "big enough" is compared to: Price (default) reads the minimum size as a fraction of the price (0.00015), Bar range reads it as a multiple of the median candle range over the last reference window candles (0.15 over 20 candles).
The two are not the same number in different clothes. A fraction of the price behaves the same on BTC and on SHIB, but not on the same market at a different timeframe: a candle on the hourly chart is three times the 15-minute one, and the threshold does not grow with it. Measuring against the median range does. Of the four concepts that offer the switch this is the one it changes least, because a gap only exists where two candles fail to overlap — the geometry already carries the scale.
Count as filled decides when the gap is used up: Touch (default) ends it when price meets the near edge; Fill waits until the whole gap is closed.
Whether a used-up gap stays on the chart (greyed out) or vanishes is not this setting — it sits at the top of the Concepts panel, for every zone.