The pattern of implied volatility across strikes at a given expiration. Plot IV against strike and you get a curve; in equities it tilts so out-of-the-money puts carry higher IV than calls. "Skew" usually refers to that tilt, but the full curve also has a height and a smile.

Because the same headline skew can move for opposite reasons. The curve can shift up (Level), tilt more (Slope), or bow out at the wings (Curvature) — and each points to a different trade. A single number blends all three, so you can't tell which risk actually changed.

That puts are richer than calls at equivalent distance from spot — normal equity put-skew. The more negative the Slope, the steeper the tilt. Slope flattens toward zero in rallies and steepens (more negative) under stress.

For equity indexes, almost always: persistent demand for downside protection, plus call overwriting, keeps index puts bid and calls offered — so the curve tilts toward puts. Single stocks are different. High-growth or takeover names — TSLA is the classic example — can carry a positive Slope, with calls richer than puts because the crowd is paying up for upside. Negative Slope is the index norm, not a universal law.

That the wings — the far-OTM options on both sides — are bid at a premium beyond what the straight-line tilt predicts. The market is paying up for the tails, not just the direction. High Curvature is the signature of priced tail risk.

It isn't, conceptually. Level is the open-interest-weighted average IV across the chain — the height of the surface — which is the same thing VolDex® measures at-the-money. Level is the deconstruction's view of the VolDex® story.

Slope drives RiskDex® (the put-vs-call tilt, via the PutDex®/CallDex® ratio). Curvature drives TailDex® (the price of the ~3-sigma OTM put). When Curvature rises in the deconstruction, expect TailDex® to rise.

The IV deviations the three components don't explain — idiosyncratic, strike-by-strike mispricing. A large residual at one strike usually means concentrated open interest or a data quirk, not a regime signal.

Matched call/put strike pairs within ±40% of spot, fit at your chosen target tenor (7 to 60 days; it resolves to the nearest listed expiration at or beyond the target). History lookback runs 30 to 180 days.

Live components come from the current options chain. The historical component series uses return-based proxies derived from daily closing returns of the underlying.

For simplicity and consistency. Dividend-paying names can show minor distortion as a result; the risk-free rate used is the 13-week U.S. Treasury bill, updated daily.

Yes — Slope and Curvature surface as RiskDex® and TailDex®, which are published Nations indexes the alert engine already monitors. So you can alert on the tilt (RiskDex®) and the tail premium (TailDex®) directly.