A situation that occurs when the underlying of an option settles near or at its strike price (exercise price) at expiration. Thus, the underlying is said to be “pinning”.

Also, pinning is the likelihood that the underlying price (such as a stock price) will coincide with the strike price of the option written on it, immediately prior to the option’s expiration date.

Pinning is often attributed to the demand for deltas by market makers at times when the open interest corresponding to a specific combination of strike and expiration is exceptionally high.