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 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 or by third parties. The most common forms of these are in doctor–patient confidentiality (physician–patient privilege), attorney–client privilege, priest–penitent privilege, and bank–client confidentiality agreements.