A call or put option whereby the holder has the retroactive right to purchase (if a call) or sell (if a put) the underlying asset at the lowest level (if a call) or the highest level (if a put) it achieves within a specified period known as the lookback period. A lookback option differs from a lookback price option in the sense that the latter gives its holder the retroactive right to cash in the option contract at the maximum value it reaches or attains within the lookback period.

In general, lookback options are path-dependent options whose payoffs depend not only on the underlying price at expiration date, but also on the maximum or minimum asset price attained over a pre-defined monitoring window (the lookback period).

A lookback option has many different names including a best strike option, a dint, a no-regrets option, a hindsight option, or a lookback strike option.