Русско-англо-русский юридический словарь

A plaintiff (Π in legal shorthand), also known as a claimant or complainant, is the term used in some jurisdictions for the party who initiates a lawsuit (also known as an action) before a court. By doing so, the plaintiff seeks a legal remedy, and if successful, the court will issue judgment in favor of the plaintiff and make the appropriate court order (e.g., an order for damages). [...]

In Hong Kong, Canada and the United States, as well as in both Northern Ireland and the Republic of Ireland, the legal term "plaintiff" is still in use. American usage traditionally limits the application of terms such as "claimant" and "claim form" to extrajudicial process in insurance and administrative law. After exhausting remedies available through an insurer or government agency, an American claimant in need of further relief would turn to the courts, file a complaint (thus establishing a real court case under judicial supervision), and become a plaintiff. (Wikipedia)

In Scottish law a plaintiff is referred to as a "pursuer" and a defendant as a "defender". (Wikipedia)

In England and Wales, the term Claimant has replaced Plaintiff after the Civil Procedure Rules 1998 came into force on 26 April 1999. (Wikipedia)