期权又称为选择权（英语：Option），有时也看作是期货和选择权的合称。选择权是一种通常可交易的衍生金融工具，根据某项资产（如股权、股票指数或期货）在未来某一时间段的价格，确定期权交易中买家的权利和卖家的义务。 简单的说，期权指的是一种在一定期限内的交易选择权，也就是赋予了持有人一种按照约定价格买或卖的权利，但是持有人可以自己决定要不要行使这个权利。在期权的交易时，购买期权的一方称作买方，而出售期权的一方则叫做卖方；买方即是权利的受让人，而卖方则是必须履行买方行使权利的义务人。

期权具「零和游戏」特性，而个股期权及指数期权皆可组合，进行套利交易或避险交易。

In finance, an option is a contract which gives the buyer (the owner or holder of the option) the right, but not the obligation, to buy or sell an underlying asset or instrument at a specified strike price on a specified date, depending on the form of the option. The strike price may be set by reference to the spot price (market price) of the underlying security or commodity on the day an option is taken out, or it may be fixed at a discount or at a premium. The seller has the corresponding obligation to fulfill the transaction – to sell or buy – if the buyer (owner) "exercises" the option. An option that conveys to the owner the right to buy at a specific price is referred to as a call; an option that conveys the right of the owner to sell at a specific price is referred to as a put. Both are commonly traded, but the call option is more frequently discussed.