Four names get used constantly in options-flow discussion: the gamma flip, the call wall, the put wall and the 0DTE walls. They are not the same thing, and each one tells you something different about where price might stall or accelerate. Here is what each means and what it typically does.
The gamma flip — sometimes called the HVL, or high-volume level — is the price where dealers' aggregate gamma exposure changes sign. It is the single most important line on the map, because it divides the session into two regimes rather than marking one spot.
Above the flip, dealers are typically long gamma: as price rises they sell, and as it falls they buy. That flow leans against the move, so the tape tends to mean-revert and pin. Below the flip, the sign reverses: dealers hedge with the move, so declines can accelerate as more selling forces more selling. Traders watch the flip because crossing it changes the character of the session, not just the next tick.
A call wall is the strike with the largest concentration of call-side dealer gamma. It is a level where rallies often stall or reverse. A put wall is the mirror image on the put side — the strike with the heaviest put gamma, and a level where declines often find support.
The intuition is the same as any gamma level. At the wall, a small move forces a large, one-directional hedge, and that hedge leans against the move. But a wall is not a guarantee: a wall that holds three sessions in a row can break in a single session when positioning changes, which is exactly why we grade every level in public rather than advertising a hit rate. We label these "walls" because that is the conventional name, not because price is walled off.
Zero-days-to-expiry options — 0DTE — are contracts that expire the same session they trade. Their gamma is enormous relative to their price, so the dealer hedging behind them is unusually intense, and it disappears by the close. That is why 0DTE walls can act strongly for a few hours and then vanish.
Two practical consequences. First, a 0DTE wall can move during the session as strikes are opened and closed, so it is a live level, not a fixed one. Second, once the expiry passes, the wall is gone and the levels behind it may be all that is left. When a 0DTE wall and a longer-dated wall sit at the same strike, the level is often described as reinforced — but "reinforced" is still a description of positioning, not a forecast.
The expected move is the session's options-implied range — roughly a one-standard-deviation envelope derived from the options market's own pricing of future volatility. It is not a gamma level, but it belongs on the same map: it answers "how far is a normal day?" so that a move to a wall can be judged as routine or unusual.
A common use is to read direction and range together. Inside the expected-move band with price above the flip, a quiet, pinning session is consistent with the structure. A push beyond the band is a signal that realised volatility is running ahead of what options were pricing, which is usually where trend sessions come from.
Mark the flip, the call and put walls, any same-strike 0DTE wall, and the expected-move band before the open. Then watch which levels actually produce a reaction. A level that holds with shrinking volume is different from one that holds with expanding volume; a wall that breaks on a close is different from one that wicks and recovers. The levels tell you where to look. The tape tells you what is happening.
See the intro to gamma levels, how to use them on NQ and ES, or how SPECTRE grades each level in public.