When the contract provides an opt out period the status is OP, indicating that the buyer could change his mind and opt out. Once that period passes there may still be some contingencies to satisfy and the status is PS, pending continue to show, indicating that back up offers are welcome due to the possibility of the first contract terminating as a result of a legitimate contingency. Once all the contingencies have passed and closing is assured the status will be P, pending.
Hope this helps clear up understanding of the various statuses.