Glossary
Options-specific
Option contract
A contract giving the buyer the right (not obligation) to buy or sell 100 shares of a stock at a fixed price (strike) by a fixed date (expiration). Calls = right to buy. Puts = right to sell. Buyer pays premium; if unused by expiration, premium is lost.
Strike
The fixed price at which the option can be exercised.
Expiration
The date the option expires. After this date the contract is worthless if not exercised or sold.
Premium
The price the option contract trades at. Quoted per share but contracts represent 100 shares (so a premium of $2.50 means you pay $250 per contract).
Open Interest (OI)
Total number of outstanding contracts at a given strike+expiration that have not been closed or expired. Indicates how widely held a strike is.
Volume
Number of contracts traded today at that strike+expiration. Compared against OI to detect unusual activity.
Implied Volatility (IV)
The market's expectation of future stock movement, derived from current option prices. Quoted as annualized %. A stock with 30% IV is "expected" to move within plus/minus 30% over the next year at 1 standard deviation. Higher IV = options more expensive.
Realized Volatility (RV)
What the stock actually did, measured from past prices. Computed as standard deviation of log returns times sqrt(252).
Greeks
Sensitivities of an option's price to different inputs.
- Delta (Δ): change in option price per $1 change in stock price. ~0.5 for at-the-money.
- Gamma (Γ): change in delta per $1 change in stock price. Highest near at-the-money.
- Theta (θ): change in option price per day from time decay. Always negative for option buyers.
- Vega (ν): change in option price per 1% change in IV.
GEX (Gamma Exposure)
Net dealer gamma in dollars per 1% spot move. Positive = dealers short gamma, hedge against trend (dampens vol). Negative = dealers long gamma, hedge with trend (amplifies vol).
Zero-GEX / flip strike
The strike where cumulative net GEX crosses zero. Often acts as an intraday pivot level.
Max pain
The strike that minimizes total option payout at expiration, weighted by current OI. Some traders use it as a magnet level near opex.
Expected move
1-day, 1-sigma expected stock movement from ATM IV. About 68% probability the stock stays within +/- this range tomorrow.
Bid / Ask / Last
Bid = highest price someone is willing to pay. Ask = lowest price someone is willing to sell. Last = price of most recent trade. Spread = ask minus bid; wide spread is bad for trade execution.
0DTE
"Zero Days To Expiration." Options expiring today. Extremely volatile near close.
OPRA
Options Price Reporting Authority. The consortium that consolidates options trade and quote data from all 16 US options exchanges. Real-time access requires paid OPRA subscription.
Skew
The difference between put IV and call IV at equivalent distances from the money. Positive skew = puts cost more (downside fear). Common in US equities.
IV term structure
IV by expiration date. Contango = back month IV higher than front month (normal). Backwardation = front month higher (near-term event risk).
Unusual flow
Single-contract trades where today's volume meaningfully exceeds open interest AND total premium spent is large. Often indicates someone opening a new position with conviction.
Wheel strategy
Sell cash-secured puts. If assigned, sell covered calls on the stock. Repeat. Generates income from premium.
Iron condor
Sell an OTM call spread plus an OTM put spread on the same expiration. Profits if stock stays within a range. Defined risk.
Vertical spread
Buy one option, sell another at a different strike (same type, same expiration). Limited risk, limited reward.
Stock and quant terms
Alpha
Returns above (or below) a benchmark, attributable to strategy skill. We measure alpha vs SPY.
Backtest
Simulating a strategy on historical data to estimate how it would have performed. Useful but not predictive of future returns.
Walk-forward backtest
Backtest that respects the arrow of time: at each historical date, the strategy only sees data that was actually available then. Prevents look-ahead bias.
Survivorship bias
Bug in backtests where you implicitly exclude stocks that went to zero or got delisted. Inflates apparent returns. Fixed by including delisted tickers in the universe.
Sharpe ratio
Risk-adjusted return: (return minus risk-free rate) divided by volatility. Higher = better.
Drawdown
Peak-to-trough decline in equity. Max drawdown is the worst one in the period.
Drift (PEAD)
Tendency of stocks to continue moving in the direction of a news shock (gap-up, earnings beat) over the following weeks. Documented by Bernard-Thomas 1989.
Momentum
Tendency of recent winners to continue winning over 3-12 month horizons. Documented by Jegadeesh-Titman 1993.
Mean reversion
Tendency of extreme moves to be partially reversed in the short term. Connors RSI(2) is a popular implementation.
Bootstrap
Statistical technique: resample your data with replacement many times to estimate confidence intervals on a metric.
Black-Scholes
The standard model for pricing European options. We use it to compute greeks from IV.
VIX
S&P 500 30-day implied volatility index. The "fear gauge." Below 15 = complacent. 15-20 = normal. 20-30 = stress. Above 30 = panic.
COT (Commitments of Traders)
Weekly CFTC report showing positioning of commercial hedgers, large speculators, and small traders in futures markets.
13F
SEC filing required from institutions managing $100M+. Discloses quarterly holdings. Used to track what big funds own.
Form 4
SEC filing required when company insiders (officers, directors, 10%+ shareholders) trade their company's stock. Must file within 2 business days.
STOCK Act
2012 US law requiring members of Congress to disclose stock trades within 45 days. Used by retail traders to track "politician trades."