Non Circumvention/Non Disclosure Agreements ensure that the intermediaries in the transaction are not cicumvented and excluded from the transaction by the Buyer and/or Seller and/or the other intermediaries.
Many trade transactions are chain-like.
Product flows like this: seller-broker-broker-broker-buyer.
The brokers in the middle use NCNDs to ensure that they are not circumvented by anyone else in the chain; also, to ensure that information on the other parties in the chain is not disclosed to outside parties.
They are valid for a specified term; usually two years.