The "termination" clause usually does not exist in the non-disclosure agreement, as it destroys the document's whole concept. However, it's possible to terminate the agreement before the end date by the parties' mutual agreement. It's usually indicated in the contract and describes how such a decision can be notified to the other party(-ies). In most cases, a prior written notice within a specific period of time is required.
Note that confidentiality obligations can be continued even after the termination of the agreement. In this case, the receiving party will also be obliged to return or/and destroy any copy of disclosed information after the NDA's termination.