Русско-англо-русский юридический словарь

In the U.S. judicial system, procedural rules require most motions to be made in writing and can require that written notice be given in advance of a motion being made. Written motions specify what action the movant is requesting and the reasons, or grounds, for the request. A written motion may contain citations to case law or statutes that support the motion. (TheFreeDictionary)

When a party makes a motion in a case, that party is called the movant. For example, if a plaintiff in a civil case moves for summary judgment, the plaintiff is the movant. (Legal Information Institute)