An IFVG is an FVG that price crossed all the way through, and which stays on the chart with the opposite sign. There was a bullish gap, price closed below its lower edge — the same range remains as a bearish zone.
On the site it is labelled "inverted gap".
How it forms
An ordinary gap lives until price returns inside it. Returning inside is not the end: the zone is marked as touched. The end comes when price passes through it entirely, to the far edge.
That is the moment the IFVG appears. Same boundaries, same size in ATR, reversed direction. The original gap is marked mitigated, and the inversion is recorded as a separate object referring back to it.
From there the inversion has a life of its own: fresh, touched or mitigated, now in the new direction. If price crosses it all the way through in the reverse direction too, no object remains. An inversion of an inversion never reaches the chart.
Why not every filled gap gives an inversion
Two conditions. First, the original gap has to be real: at least 0.3 ATR, otherwise it would never have been drawn. Second, the inversion must still be alive at calculation time — if price went straight through it after the flip, no object is created.
So there are noticeably fewer inversions on a chart than filled gaps, and that is normal.
How it differs from a BPR
An IFVG comes from one gap that flipped. A BPR comes from two different gaps, one bullish and one bearish, that overlap in price. All they have in common is that both are built on gaps.
What the zone does not mean
An inversion says exactly one thing: this range was an untraded stretch in one direction, and later price crossed it in the other. That is a fact about the past.
The markup makes no claim that price will return to an inversion or that it now "acts as resistance". How many such zones get tested again is a question of statistics for a particular instrument.