In legal terminology, a complaint is any formal legal document that establishes the facts and legal reasons for a lawsuit. A complaint must list the reasons for the plaintiff's case, and it must ask for a specific legal remedy. Once a complaint is filed with the court a summons (an order from the court) is notifies the defendant a lawsuit has been filed against them. Once a defendant receives notice of a complaint, they must reply within a specified period of time with an answer. Complaints are pleadings that must be written carefully to properly state the facts and legal basis for the claim. Usually this requires the help of an attorney.
In some jurisdictions, specific types of criminal cases may also be started by the filing of a complaint. This is also called a criminal complaint or felony complaint. All criminal cases are prosecuted in the name of the governmental authority. This is the same authority whose criminal laws were broken and who enforces criminal statutes. The government is sometimes called the state, the People or the Crown (in Commonwealth realms). In the United States, the complaint is often associated with misdemeanor charges presented by the prosecutor without the grand jury process. In most US jurisdictions, the document presented to and authorized by a grand jury is called an indictment.