The strike level at which a barrier product (e.g., a barrier option) either becomes effective (in which case, it is an instrike) or ineffective (as an outstrike).

An instrike is the underlying price at which knock-in options become standard options, i.e., effective and able to pay off, in case that price hits or trades through a specific upper or lower barrier under certain circumstances as set out in the contract. Knock-in options comprise mainly down-and-in calls/ down-and-in puts and up-and-in calls/ up-and-in puts.

An outstrike is the underlying price at which knock-out options expire or pay off in case that price hits or trades through a specific barrier under certain circumstances as set out in the contract. Knockout options consist mainly of down-and-out calls/ down-and-out puts and up-and-out calls/ up-and-out puts.