In general use, a complaint is an expression of displeasure, such as low quality service at a store, or from a local government, etc. In legal terminology, a complaint is a formal legal document that sets out the facts and legal reasons (see: cause of action) that the filing party (the plaintiffs) believes are sufficient to support a claim against another person, persons, entity or entities (the defendants) that entitles the plaintiff(s) to a remedy (either money damages or injunctive relief). For example, the Federal Rules of Civil Procedure that govern civil litigation in United States courts provide that a civil action is commenced with the filing or service of a pleading called a complaint. Civil court rules in states that have incorporated the Federal Rules of Civil Procedure use the same term for the same pleading.
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