In finance, a binary option is a type of option in which the payoff can take only two possible outcomes, either some fixed monetary amount (or a precise predefined quantity or units of some asset) or nothing at all (in contrast to ordinary financial options that typically have a continuous spectrum of payoff). The two main types of binary options are the cash-or-nothing binary option and the asset-or-nothing binary option.

The cash-or-nothing binary option pays some fixed amount of cash if the option expires in-the-money while the asset-or-nothing pays the value of the underlying security. They are also called all-or-nothing options, digital options (more common in forex/interest rate markets), and fixed return options (FROs) (on the American Stock Exchange).[1]

For example, a purchase is made of a binary cash-or-nothing call option on XYZ Corp’s stock struck at $100 with a binary payoff of $1,000. Then, if at the future maturity date, often referred to as an expiry date, the stock is trading at above $100, $1,000 is received. If the stock is trading below $100, no money is received. And if the stock is trading at $100, the money is returned to the purchaser.  The value of a digital option can be expressed in terms of the probability of exceeding a certain value, that is, the cumulative distribution function, which in the Black-Scholes equation is the Gaussian.

Due to the difficulty for market-makers to hedge binary options that are near the strike price around expiry, these are much less liquid than vanilla options. Dealers often replicate them using vertical spreads, which provides a rough, inexact hedge.  Though binary options sometimes trade on regulated exchanges, they are generally unregulated, trading on the internet, and prone to fraud.[1] The U.S. Securities and Exchange Commission (SEC) and Commodity Futures Trading Commission (CFTC) have issued a joint warning to American investors regarding unregulated binary options.[2]