Definition - What does Complaint mean?
A complaint is the official document that is filed with a court to initiate legal action against another party. With a civil complaint, one party (the plaintiff) is claiming that another party has committed a civil wrong against him or her. With a criminal complaint, one party is claiming that another party (the defendant) has committed a criminal wrong against him or her, or has committed a crime in general.
Justipedia explains Complaint
A complaint is really the thing that starts the legal process. Without complaints, there would be no trials, because no one would be trying to claim that a law has been broken, or that damages are owed for losses accrued.
However, just because a complaint is filed does not automatically mean that the person filing the claim will win the case, or that he or she is even accurate about his or her complaint.
For example, one person may file a complaint against another person for copyright infringement. However, in the course of the case, it may be discovered that the copyright had already expired, and that therefore the plaintiff had no case. Complaints only begin the legal process. It is trials that result in facts being judged.