A gamma wall is a strike with very large options open interest where dealer gamma concentrates. Because market makers must hedge that exposure, price tends to be pulled toward the wall and pin near it — so it acts like a magnet and, often, support or resistance.
Market makers must stay delta neutral, so as price moves they buy or sell the underlying to offset the options they hold. Near a large or fast-growing wall, that forced flow is significant and predictable — it can pin price, or, when the wall grows quickly, push it.
0DTE options expire the same day. Their gamma near expiration is extreme, so dealer hedging and price become highly reactive to order flow. Sudden size on a normally-dead 0DTE strike is one of the clearest signals that something is happening.
It means dealers hold no net directional bet — they continuously trade the underlying to cancel out the delta of their options book. That constraint, not any market view, is what generates the repeatable hedging flow you can position around.
The gamma flip level is the price where aggregate dealer gamma changes sign. Above it, dealers dampen moves (buy dips, sell rips); below it, they amplify moves (sell rallies). Crossing it often marks a change in how the tape behaves.
Look for relative volume, not absolute size: a spike versus a strike's own recent baseline. Sustained abnormal volume beats a single flash, correlated bursts across nearby strikes strengthen the signal, and agreement with an independent trigger (like a technical cross) is the strongest confirmation.