The King County (WA) Law Library has an excellent: Debt Collection Lawsuit Research Guide. The state law links are to Washington State laws, but the other information and federal law links apply to everyone. There is also a podcast with additional information on this subject.
Excerpt from the research guide: “What is a Debt Collection Lawsuit?
A debt is a sum of money owed by one person to another. A lawsuit is a legal action by one person or entity against another person or entity, which is decided in a court of law. A debt collection lawsuit is started in a court by a “cause of action” as the particular amount of money owed. The person or entity starting the lawsuit is the plaintiff. (Definition from: http://dictionary.law.com/).