NDA / non-disclosure agreementNDA / non-disclosure agreement: a legal agreement between tw...: a legal agreement between two or more parties that requires certain information that passes between the parties to be kept confidential and only used for certain limited purposes, such as to enable the parties to evaluate the possibility of entering into a business relationship; also known as a confidentiality agreement. NDA’s have many different commercial law applications and are an important tool for businesses seeking to protect sensitive business information and trade secrets.