0DTE Options

0DTE options are contracts on their final day before expiration ('zero days to expiration'). In indices like the S&P 500 they trade in enormous volume, and because their gamma is extremely concentrated near the current price, dealer hedging of 0DTE flow can strongly shape intraday moves.

25-Delta Skew

The 25-delta skew is a standard convention for quantifying volatility skew: the difference in implied volatility between the option whose delta is near 0.25 on the put side and the option whose delta is near 0.25 on the call side, at the same expiration. Because it condenses the full skew curve into one comparable figure, it is the number most often quoted when traders describe skew as steepening or flattening.

Call Wall

A call wall is the strike above the current price with the largest concentration of call open interest. Because dealers are often short those calls and long gamma there, their hedging can slow advances into the strike, so it frequently behaves as a near-term ceiling.

Charm (Delta Decay)

Charm is the rate at which an option's delta changes as time passes, holding price constant. Because charm steadily shifts dealers' hedges as expiration approaches, it produces predictable, time-of-day hedging flows - often visible into the close and into Friday expirations.

Dark Pool Flow

Dark pool flow refers to equity trades executed on private trading venues away from the public, lit exchanges, and reported after the fact under standard trade-reporting rules rather than shown pre-trade. Because dark pools let large institutional orders trade with less immediate market impact, dark pool prints are read as a proxy for the size and direction of positioning that a fully public order book would reveal too early.

Dealer Delta Exposure (DEX)

Dealer delta exposure (DEX) is an estimate of the net directional exposure option dealers carry across the chain, built by aggregating each contract's delta weighted by open interest and signed by the estimated dealer side. Where gamma exposure describes how a dealer's hedge must change as price moves, DEX describes the size and direction of the hedge dealers are estimated to be carrying right now.

Dealer Gamma Positioning (Long vs. Short Gamma)

Dealer gamma positioning describes whether option market-makers are net long or net short gamma. Long-gamma dealers hedge against the move (buy dips, sell rips), which dampens volatility. Short-gamma dealers hedge with the move (sell dips, buy rips), which amplifies volatility.

Dealer-Directional Open Interest (DDOI)

Dealer-directional open interest (DDOI) is open interest broken out by strike and signed according to which side of the trade dealers are estimated to hold, long or short, rather than reported as a single unsigned contract count. Where raw open interest only reports how many contracts exist at a strike, DDOI adds the estimated directional read that turns a contract count into a hedging-flow estimate.

Delta

Delta measures how much an option's price is expected to change for a one-point move in the underlying, ranging from 0 to 1 for calls and -1 to 0 for puts. A 0.50-delta call gains roughly half a point for every one-point rise in the underlying. Delta also serves as a rough hedge ratio and an informal proxy for the probability an option finishes in the money.

Delta Hedging

Delta hedging is how option dealers neutralize directional exposure: delta measures how much an option's value changes per one-point move in the underlying, and dealers buy or sell the underlying to offset the aggregate delta of their book. That continuous re-hedging is the transmission mechanism between options positioning and the underlying's price action.

Expected Move

The expected move is the market-implied one-standard-deviation range for the underlying over a given horizon, commonly estimated from the price of the at-the-money straddle. The 0DTE chain publishes a same-day expected move every morning - the options market's own estimate of that session's range.

Gamma

Gamma measures how much an option's delta changes for a one-point move in the underlying - the rate of change of delta, or delta's own sensitivity to price. Gamma is largest for at-the-money options nearing expiration, and it is the mechanism that forces dealers to continuously re-hedge, the basis of gamma exposure (GEX).

Gamma Exposure (GEX)

Gamma exposure (GEX) is an estimate of how much option market-makers must buy or sell the underlying to stay hedged as its price moves, aggregated across strikes. When dealer GEX is net positive, hedging tends to dampen price moves; when it is net negative, hedging tends to amplify them.

Gamma Squeeze

A gamma squeeze is a self-reinforcing move driven by dealer hedging of concentrated short-gamma exposure: as price rises toward heavily-bought call strikes, dealers hedging those short calls must buy the underlying, pushing price further and forcing still more buying. The loop runs until the positioning clears or expires.

Implied Volatility (IV)

Implied volatility is the level of future movement an option's market price implies - the volatility input that makes a pricing model match what the option actually trades for, expressed as an annualized percentage. It is the market's priced-in expectation of movement, not a forecast that must come true.

IV Crush (Volatility Crush)

IV crush is the rapid deflation of implied volatility - and with it, option prices - once an anticipated event passes or uncertainty resolves. Because the event premium drains out of every contract at once, a trader can be right on direction and still lose money owning options through the event.

Max Pain

Max pain is the strike at which the total value of outstanding options would be lowest at expiration - the point of maximum aggregate loss for option buyers. The popular theory holds that price gravitates there into expiry; where such a pull exists, it is better explained by dealer hedging around large open interest than by any deliberate targeting.

Net Gamma Exposure

Net gamma exposure is the single aggregate figure produced by combining call-side and put-side gamma exposure, with their respective sign conventions, across every strike and expiration into one number. It is the headline figure typically quoted for 'the market's GEX today' - positive or negative, in dollars per one-percent move - distinct from the per-strike profile that shows where that exposure actually concentrates.

Open Interest (OI)

Open interest is the number of option contracts currently outstanding at a strike and expiration - positions opened but not yet closed, exercised, or expired. Unlike volume, which counts trading activity, OI measures standing exposure, and its concentration across strikes is the raw material for wall, pin, and gamma estimates.

OPEX (Options Expiration)

OPEX refers to scheduled options expirations - most notably the monthly third-Friday cycle and the quarterly 'triple witching' - when large blocks of open interest leave the board at once. Because expiring positions take their dealer hedges with them, the sessions around OPEX often reset the market's structure and can change its volatility regime.

Options Order Flow

Options order flow is the stream of executed option trades, read for who initiated each trade (buyer or seller), with what urgency (sweeps, blocks), and at which strikes - to infer how positioning is building. Aggregated flow is one of the inputs behind dealer-positioning estimates, and one of the easiest datasets to over-read.

Pin Risk / Pinning

Pinning is the tendency for the underlying to gravitate toward a strike with very large open interest as expiration approaches, because dealer hedging around that strike compresses price toward it. Pin risk is the uncertainty of whether options finish just in or out of the money at that pinned level.

Put Wall

A put wall is the strike below the current price with the largest concentration of put open interest. Dealer hedging around that strike can slow declines into it, so it frequently behaves as a near-term support cushion.

Put/Call Ratio

The put/call ratio divides put activity by call activity, using either volume or open interest, as a rough gauge of hedging and fear versus speculative appetite. Readings near long-run averages carry little signal; extremes are often read contrarian - panicked put-buying has historically clustered near lows rather than ahead of them.

Realized vs. Implied Volatility

Realized volatility measures how much the underlying actually moved over a past window; implied volatility is what options currently price for future movement. The spread between them - implied usually sits above realized - is the volatility risk premium, and its widening or collapse is one of the cleanest regime signals in options markets.

Speed and Color

Speed and color are third-order option Greeks. Speed measures how fast an option's gamma changes as the underlying moves - the rate of change of gamma with price. Color measures how gamma changes as time passes - the rate of change of gamma with time. Both are small for most positions but become meaningful for very short-dated, near-the-money options, where gamma itself is already large and unstable.

SPX vs. SPY Options

SPX options are cash-settled, European-style contracts on the S&P 500 index itself, roughly ten times the notional of SPY options - which are physically-settled, American-style options on the ETF. Settlement, exercise style, and size differences change how each chain trades and how it is analyzed.

Strike Price

The strike price, or exercise price, is the fixed price at which an option contract's holder has the right to buy (a call) or sell (a put) the underlying. Every option chain lists a ladder of strikes around the current price, and where open interest concentrates on that ladder - producing the call and put walls - is one of the central inputs to options market-structure analysis.

Theta (Time Decay)

Theta is the rate at which an option's value declines as time passes with everything else unchanged, usually quoted per day. Option buyers pay theta; option sellers collect it. In 0DTE contracts theta is at its extreme - the entire remaining time value decays within a single session.

Vanna

Vanna measures how an option's delta changes when implied volatility changes. Because a shift in volatility alters dealers' hedges even when price is flat, vanna links the volatility surface to spot: falling volatility can create a mechanical bid as dealers re-hedge, a dynamic often behind grind-higher, vol-compressing rallies.

Variance Risk Premium

The variance risk premium (VRP) is the amount by which implied volatility, priced into options today, has tended to exceed the realized volatility that subsequently occurs. It reflects the price buyers are willing to pay for protection against unpredictable moves - a structural premium that, averaged over long samples, has historically made systematically selling volatility a profitable, though not risk-free, activity.

Vega

Vega measures how much an option's price changes for a one-point change in implied volatility. Long options are long vega (they gain when implied volatility rises); short options are short vega. Vega is the channel through which the market's changing expectation of movement reprices every contract on the chain.

VIX Term Structure

The VIX term structure is the curve formed by implied volatility across different horizons, from the front-month VIX futures contract out to longer-dated ones. Under normal conditions the curve slopes upward - contango, with longer-dated volatility priced higher - while during acute market stress it can invert into backwardation, with near-term volatility priced highest, a pattern widely read as a stress signal.

Volatility Regime

A volatility regime is the prevailing character of market moves - dampened and range-bound, or amplified and trending. In options market structure, the regime is closely tied to dealer gamma positioning: a positive-gamma regime compresses moves, while a negative-gamma regime amplifies them.

Volatility Skew

Volatility skew is the pattern of implied volatility differing across strikes of the same expiration. In equity indices like the S&P 500, downside puts almost always trade at higher IV than upside calls, reflecting persistent demand for crash protection. Changes in the skew's steepness are read as shifts in hedging demand.

Vomma (Volga)

Vomma, also called volga, measures how much an option's vega changes as implied volatility itself changes - vega's own sensitivity to volatility. It is largest for far out-of-the-money options and matters most when implied volatility itself is moving sharply, such as around volatility spikes.

Zero-Gamma / Gamma Flip Level

The zero-gamma or gamma flip level is the estimated underlying price at which the dealer complex's net gamma switches sign. Above it, dealers are often net long gamma (volatility-dampening); below it, net short gamma (volatility-amplifying). It marks the boundary between the two regimes.