A more thorough explanation:

A civil investigative demand is a request for information made by the U.S. Attorney General or a state attorney general to any person who may have documents or information relevant to a civil antitrust investigation or an investigation authorized by the International Antitrust Enforcement Assistance Act. This demand can be issued before a civil or criminal action is initiated and can be served on anyone who is believed to possess information pertinent to the investigation.

For example, if the U.S. Attorney General is investigating a company for antitrust violations, they may issue a civil investigative demand to the company's competitors, suppliers, or customers to gather information about the company's business practices.

If the Attorney General begins a civil or criminal action, this demand may not be served on persons within the scope of the proceeding. This means that if a person or company is already involved in the legal proceedings, they cannot be served with a civil investigative demand.

A similar request for information can also be made by a state attorney general. This is known as a state civil investigative demand or state CID.

For example, if a state attorney general is investigating a company for consumer fraud, they may issue a state CID to the company's employees or customers to gather information about the company's business practices.