In the US, a legally binding contract must consist of:
An offer from one party
Acceptance of that offer from another party
Consideration from the party accepting the offer
The mutual acceptance of both parties to be bound by
A non-disclosure agreement (NDA) (1) is a contract
between parties wherein either one or
both parties agree to keep specific information
from the other party a secret.
(1) Link to https://everynda.com/blog/sample-non-disclosure-agreement-template/
A good NDA can have different terms of "duration".
A term for the contract itself, which is the effective
period of the agreement
And a term for how long confidentiality obligations
are expected to apply for.
In this example clause from Accuride Corp’s (2)
Confidentiality and Non-Disclosure Agreement shows
that the five year confidentiality period starts from
the date of the agreement itself.
(2) Link to http://www.accuridecorp.com/files/2012/09/ConfidentialityNondisclosureAgreement.pdf
The "termination" clause will generally specify:
How the intention to terminate should be
communicated to the other party (for example, in writing)
And whether any notice period is required
before termination kicks into effect
Example of a clause taken from a mutual NDA
where 30 days written notice is required and the
obligation of confidentiality is to continue for five
years after the termination of the agreement:
A "Return of Confidential Information" clause is used
to specify that the other party is required to:
To return all information back to you
To destroy all copies of information in their possession
To show you confirmation that they have done so
And perhaps also, to agree not to make any further
copies from then onwards.
And so on