Civil procedure is the written set of rules that sets out the process that courts will follow when hearing cases of a civil nature (a "civil action"). These rules explain how a lawsuit must be commenced, what kind of service of process is required, the types of pleadings, motions, and orderss allowed in civil cases, the timing and manner of depositions and discovery, the conduct of trials, the process for judgment, various available remedies, and how the courts and clerks must function.
In the United States, the model for most state courts is the Federal Rules of Civil Procedure, first adopted on September 16, 1938 before which time there were varying rules that governed different types of civil cases such as cases at law or in equity or in admiralty. There are exceptions to the types of cases that these rules now control but they are few in number and somewhat esoteric (e.g., "prize proceedings in admiralty").
See also: Affirmative defense, Answer, Cause of action, Summons, Jurisdiction, Laches, Motion, Strategic lawsuits agains public participation, Statute of limitations, Time constraints, Trial de novo, Vexatious litigation, With prejudice