It stands for multiperiod strike reset option; an option in which the strike price is periodically reset with multiple payouts. This option pays off the greater of zero or the sum of periodical returns, each capped at a specific level. The strike price is reset in line with changes in the price of the underlying asset on pre-set dates. The option holder can lock in gains attained during the option’s life, at each point that the strike is reset, while continuing to maintain risk exposure protection.

This structure is also known as a cliquet option.