The process of being read into a compartmented program

Compartmentalization (intelligence)

In matters concerning information security, whether public or private sector, compartmentalization is the limiting of access to information to persons or other entities who have a need to know it in order to perform certain tasks....

 generally entails being approved for access to particularly sensitive and restricted information about a classified program

Classified information

Classified information is sensitive information to which access is restricted by law or regulation to particular groups of persons. A formal security clearance is required to handle classified documents or access classified data. The clearance process requires a satisfactory background investigation...

, receiving a briefing about the program, and formally acknowledging the
briefing, usually by signing a non-disclosure agreement

Non-disclosure agreement

A non-disclosure agreement , also known as a confidentiality agreement , confidential disclosure agreement , proprietary information agreement , or secrecy agreement, is a legal contract between at least two parties that outlines confidential material, knowledge, or information that the parties...

 describing restrictions on the handling and use of information concerning the program. Officials with the required security clearance

Security clearance

A security clearance is a status granted to individuals allowing them access to classified information, i.e., state secrets, or to restricted areas after completion of a thorough background check. The term "security clearance" is also sometimes used in private organizations that have a formal...

 and a need to know

Need to know

The term "need to know", when used by government and other organizations , describes the restriction of data which is considered very sensitive...

 may be read into a covert operation

Covert operation

A covert operation is a military, intelligence or law enforcement operation that is carried clandestinely and, often, outside of official channels. Covert operations aim to fulfill their mission objectives without any parties knowing who sponsored or carried out the operation...

 or clandestine operation

Clandestine operation

A clandestine operation is an intelligence or military operation carried out in such a way that the operation goes unnoticed.The United States Department of Defense Dictionary of Military and Associated Terms defines "clandestine operation" as "An operation sponsored or conducted by governmental...

 they will be working on. For codeword–classified programs, an official would not be aware a program existed with that codeword until being read in, because the codewords themselves are classified.