An option is a standardized contract granting its buyer the right, but not the obligation, to buy or sell a fixed quantity of an underlying asset at a set price within a set time — paid for upfront by a non-refundable premium. Two contract types cover every position: a call confers the right to buy; a put confers the right to sell. The defining feature of the instrument is asymmetry: the buyer (holder/long) holds an optional right and can lose at most the premium, while the seller (writer/short) takes the premium upfront and accepts an obligation to perform if the holder exercises. This section establishes the shared vocabulary — calls and puts, contract mechanics, moneyness, the intrinsic/extrinsic value split, and the exercise/expiration lifecycle — that the rest of the Derivatives & Options branch builds on. Its four child nodes carry the depth; this overview frames them and how they fit together.

The core mechanics

Standard contract terms (U.S. listed equity options).

• Multiplier: one contract represents 100 shares of the underlying. A premium quoted as $0.50 therefore costs $50 per contract; a $5.00 quote costs $500 (OCC equity-option specs; Option Alpha).
• Strike price (K): the fixed price at which the underlying can be bought (call) or sold (put) if exercised.
• Expiration: the date the contract ceases to exist. After it, the option is either exercised/settled or lapses worthless.
• Premium: the market price of the right itself, paid by buyer to seller. It is the buyer's maximum loss and the seller's maximum gain.
• Style/settlement: U.S. single-name equity options are American-style (exercisable any day to expiration) and physically settled (shares change hands); broad index options (SPX, NDX) are typically European-style and cash-settled. Detailed in the Expiration & Settlement child.

The four primitive positions and their risk shapes (Investopedia; Macroption):

The asymmetry is the whole point: buyers have capped, known risk and convex payoff; sellers have capped gain and large (sometimes unbounded) tail risk, compensated by collecting premium. Every multi-leg strategy in the rest of the branch is a combination of these four primitives.

Moneyness — the strike-vs-spot relationship

Moneyness classifies an option by where the underlying spot price (S) sits relative to the strike (K) — equivalently, whether exercising right now would pay off. For a call: in-the-money (ITM) if S > K, at-the-money (ATM) if S ≈ K, out-of-the-money (OTM) if S < K. For a put the inequalities flip (ITM if S < K). Moneyness is the first lever in strike selection because it sets the trade's entire leverage/probability/decay character: deep-ITM options behave almost like the stock (high delta, little time value), ATM options carry the most time value and volatility sensitivity, and OTM options are cheap, low-probability, lottery-like. A common heuristic — delta ≈ probability of finishing ITM — is useful for sizing strikes but is an approximation, not a measured edge. Full treatment in the In/At/Out of the Money child.

Premium decomposition — intrinsic vs extrinsic value

Every premium splits, by arithmetic identity, into two parts:

Premium = Intrinsic value + Extrinsic (time) value

Intrinsic value is the amount already in-the-money: max(S − K, 0) for a call, max(K − S, 0) for a put — floored at zero, never negative. Extrinsic value (time value) is everything paid above that: the market's price for optionality, the chance the option moves further into profit before expiry. Extrinsic value is largest at-the-money, rises with more time and higher implied volatility, and decays non-linearly to exactly zero at expiration (the "wasting asset"). The buyer fights this decay; the seller harvests it. This split is the diagnostic foundation of every options strategy — it tells you instantly how much of a premium is "hard" worth versus wasting hope. Depth in the Intrinsic vs Extrinsic Value child.

The lifecycle — exercise, assignment, expiration, settlement

An option's life ends one of three ways: it is closed (sold/bought back before expiration — by far the most common outcome), exercised, or it expires worthless. The OCC has historically stated only roughly 7% of positions are actually exercised; most are closed or lapse (OptionsEducation.org — flagged as an approximate, oft-misread figure).

• Exercise is the holder's right; assignment is the writer's obligation, allocated randomly through the OCC. The long controls whether and when; the short only finds out after the fact — so practical risk concentrates on the short side.
• At U.S. equity expiration, exercise-by-exception auto-exercises any option finishing $0.01 or more ITM unless the holder instructs otherwise (OCC; brokers may use their own thresholds).
• Early exercise of American options is usually irrational (it throws away time value); the main exceptions are deep-ITM calls before an ex-dividend date and deep-ITM puts when interest carry favors it.
• Pin risk — the underlying closing right at a short strike — is the classic expiration trap, since after-hours moves between the 4:00 p.m. close and the ~5:30 p.m. exercise cutoff can flip the outcome.

Mechanics detailed in the Assignment & Exercise and Expiration & Settlement children.

Strengths & limitations

Options add genuine capabilities equities cannot: defined-risk directional bets, leverage, income from premium-selling, and precise hedging. Their cost is complexity — three or more variables (direction, time, volatility) must all cooperate, not just direction. The single most common beginner misuse is buying cheap short-dated OTM options for leverage and losing to time decay even when mildly right on direction — the underlying must move enough and fast enough to outrun theta. On the seller's side, the mirror error is treating harvested premium as risk-free yield while ignoring the fat tail. Critically, none of this section's content is an "edge" claim: option pricing is a near-fair game before costs under efficient markets — the value here is the vocabulary and risk framing, not a prediction that any position profits.

Sources

• OCC — Equity Options Product Specifications and Characteristics and Risks of Standardized Options (100-share multiplier, standardization, exercise/assignment process).
• Option Alpha — Option Contract Multiplier (premium × 100 to actual cost).
• FINRA — Trading Options: Understanding Assignment (rights vs obligations; random allocation; American vs European; settlement).
• Investopedia / Macroption — long call, long put, short call, short put payoff and max-loss/max-gain profiles.
• OptionsEducation.org (OCC/OIC) — exercise-by-exception $0.01 threshold; ~7% historical exercise rate (flagged approximate).
• Child nodes (this tree): Intrinsic vs Extrinsic Value, In/At/Out of the Money, Assignment & Exercise, Expiration & Settlement — for full depth on each topic summarized above.