A non-disclosure agreement (NDA), also known as a confidentiality agreement (CA), confidential disclosure agreement (CDA), proprietary information agreement (PIA) or secrecy agreement (SA), is a legal contract or part of a contract between at least two parties that outlines confidential material, knowledge, or information that the parties wish to share with one another for certain purposes, but wish to restrict access to. Doctor–patient confidentiality (physician–patient privilege), attorney–client privilege, priest–penitent privilege and bank–client confidentiality agreements are examples of NDAs, which are often not enshrined in a written contract between the parties.