An option which gives its holder the right to exercise on the best or worst return earned on two or more assets or indexes during a designated time to expiration. This option, whether a call or a put, is designed to mitigate risks associated with putting options on multiple assets which have correlated returns. For the option to offer a payoff, the underlying assets need to move in the same direction.

This option has a number of variations including best-of option, worst-of option, better-of-two-assets option, worst-of-two-assets option, either-or option, alternative option, min-max option, multi-asset option, multi-factor option, and rainbow option.