Notification by The Options Clearing Corporation (OCC) to a clearing member and the writer of an option that an owner of the option has exercised the option and that the terms of settlement must be met. Assignments are made on a random basis by the OCC. The writer of a call option is obligated to sell the underlying asset at the strike price of the call option; the writer of a put option is obligated to buy the underlying at the strike price of the put option.