Glossary

Definitions for the terms used across 0DTESPX.com. Linked pages go deeper.

Instruments and the market

0DTE — Zero days to expiration. An option that expires the same trading day. See 0DTE & SPX options.

SPX — Options on the S&P 500 index: cash-settled, European-exercise, listed every trading day.

Call / Put — A call gains value as the underlying rises above the strike; a put gains value as it falls below.

Strike — The fixed price at which an option settles.

Expiration — When the option resolves. For 0DTE SPX, the 4:00 PM ET close.

Underlying — The instrument an option is based on (here, the SPX index).

Moneyness — Where the strike sits relative to the underlying: in the money (ITM), at the money (ATM), or out of the money (OTM).

Option chain — The grid of all strikes with their calls and puts. See Option chain & Greeks.

Bid / Ask / Mid — The best buy price, best sell price, and their midpoint. Market orders fill at the natural price (ask buying, bid selling); limit and stop executions are priced from the mid. See Orders.

Expected move — The size of the move the option market implies for the underlying by expiration, derived from option prices. See Market data & charts.

Intrinsic value — What an option would be worth if it expired right now: the amount it is in the money (zero for ATM and OTM options).

Extrinsic value — The part of an option's price above its intrinsic value; time value that decays to zero by expiration.

The Greeks

Delta — Sensitivity to a $1 move in the underlying (decimal 0–1; signed by position direction).

Gamma — The rate of change of delta.

Theta — Time decay per day (negative for long options, positive for short).

Vega — Sensitivity to a 1% change in implied volatility.

Implied volatility (IV) — The market's expected volatility, as an annualized decimal (0.142 = 14.2%).

Theoretical price — A model price derived from the Greeks, used when no live quote is available.

Orders and positions

Leg — One instrument within an order. Multi-leg orders combine several.

Market / Limit / Stop order — Fill now at the mid / fill only at a chosen price / trigger at a price then fill. See Orders.

Debit / Credit — Cash out (net buying) / cash in (net selling).

Multi-leg order — A spread, condor, or other structure submitted and filled atomically.

Vertical spread — Two options of the same type and expiration at different strikes, one bought and one sold; both risk and profit are capped.

Iron condor — A four-leg structure selling an OTM call spread and an OTM put spread; profits if the underlying stays between the short strikes.

Position — A holding aggregated by instrument and direction, with live P&L and Greeks. See Positions & P&L.

Net delta — The sum of delta across all positions; your directional exposure.

Payoff chart — A plot of profit/loss versus the underlying price for your positions.

Money and risk

Realized / Unrealized P&L — Locked-in gain/loss from closed positions and settlement / mark-to-market on open positions.

Net liquidation value — opening balance + the day's total P&L.

Buying power — Available capital after margin is reserved against short positions. See Buying power & margin.

Maintenance margin — Capital reserved against open shorts, per FINRA-style rules.

Fees — Per-leg brokerage charges applied to every order. See Fees.

Slippage — A per-account execution-drag setting (a multiple of $0.05) that worsens limit and stop fills in the market maker's favor, applied identically in practice, live trading, and backtests. See Orders.

Settlement — End-of-day resolution of open options at the 4:00 PM ET close. See End-of-day settlement.

Platform

Account — A persistent, cash-only trading container with a continuous balance that carries day to day, used for live trading (broker engines and bots coming soon). Replaying past days doesn't use an account — see Practice. See Accounts & trading days.

Practice — The account-less sandbox for past trading days: each day is a one-click, fixed $100,000 session with full control of the clock. See Practice.

Replay — The read-only review of a live account's settled day: scrub the clock through the day you actually traded. See Reviewing a settled day.

Session (trading day) — One trading day: a chosen past date (practice, account-less) or today under a live account. Orders, positions, transactions, and the equity curve all live under a session.

Cash balance — An account's settled carry; the cash that has rolled day to day. It never folds in an in-progress day's unrealized P&L.

Strategy — A reusable, testable definition of entries and exits, made with the builder. Immutable once saved; clone it to iterate.

Backtest — A replay of a strategy across the full history with performance metrics. See Strategy results.

Portfolio — A named collection of saved strategies whose results are aggregated at read time, each member an equal $100k sleeve. See Portfolios.

Bot — A dedicated account that runs a saved strategy hands-free against the live session, with a risk policy and automatic order re-pricing. Coming soon. See Trading bots.

Access — Visitors can watch the most recent session; a free account unlocks everything. See Access & accounts.